shell: Add doxygen
shell: Add doxygen

Closes #577.

phiros/RIOT,neumodisch/RIOT,automote/RIOT,altairpearl/RIOT,chris-wood/RIOT,rakendrathapa/RIOT,patkan/RIOT,TobiasFredersdorf/RIOT,authmillenon/RIOT,malosek/RIOT,katezilla/RIOT,kaspar030/RIOT,DipSwitch/RIOT,beurdouche/RIOT,Darredevil/RIOT,immesys/RiSyn,phiros/RIOT,DipSwitch/RIOT,Osblouf/RIOT,yogo1212/RIOT,mtausig/RIOT,sumanpanchal/RIOT,thiagohd/RIOT,centurysys/RIOT,ximus/RIOT,PSHIVANI/Riot-Code,MarkXYang/RIOT,syin2/RIOT,nsol-nmsu/RIOT,gbarnett/RIOT,thomaseichinger/RIOT,dkm/RIOT,shady33/RIOT,Yonezawa-T2/RIOT,kaleb-himes/RIOT,msolters/RIOT,AnonMall/RIOT,asanka-code/RIOT,OTAkeys/RIOT,mziegert/RIOT,ks156/RIOT,alignan/RIOT,arvindpdmn/RIOT,dhruvvyas90/RIOT,immesys/RiSyn,x3ro/RIOT,ant9000/RIOT,gbarnett/RIOT,koenning/RIOT,watr-li/RIOT,locicontrols/RIOT,zhuoshuguo/RIOT,katezilla/RIOT,MarkXYang/RIOT,attdona/RIOT,jferreir/RIOT,gautric/RIOT,rfuentess/RIOT,Ell-i/RIOT,Hyungsin/RIOT-OS,basilfx/RIOT,rajma996/RIOT,arvindpdmn/RIOT,roberthartung/RIOT,thomaseichinger/RIOT,EmuxEvans/RIOT,rfswarm/RIOT,LudwigKnuepfer/RIOT,arvindpdmn/RIOT,haoyangyu/RIOT,roberthartung/RIOT,ThanhVic/RIOT,arvindpdmn/RIOT,AnonMall/RIOT,ThanhVic/RIOT,JensErdmann/RIOT,PSHIVANI/Riot-Code,Hyungsin/RIOT-OS,benoit-canet/RIOT,OlegHahm/RIOT,haoyangyu/RIOT,PSHIVANI/Riot-Code,gebart/RIOT,neiljay/RIOT,binarylemon/RIOT,PSHIVANI/Riot-Code,chris-wood/RIOT,backenklee/RIOT,brettswann/RIOT,jferreir/RIOT,plushvoxel/RIOT,brettswann/RIOT,automote/RIOT,rfswarm2/RIOT,EmuxEvans/RIOT,robixnai/RIOT,wentaoshang/RIOT,MohmadAyman/RIOT,stevenj/RIOT,rakendrathapa/RIOT,locicontrols/RIOT,BytesGalore/RIOT,alignan/RIOT,Darredevil/RIOT,sgso/RIOT,watr-li/RIOT,rajma996/RIOT,Josar/RIOT,RubikonAlpha/RIOT,khhhh/RIOT,d00616/RIOT,emmanuelsearch/RIOT,latsku/RIOT,mfrey/RIOT,ntrtrung/RIOT,josephnoir/RIOT,herrfz/RIOT,kushalsingh007/RIOT,Darredevil/RIOT,basilfx/RIOT,jbeyerstedt/RIOT-OTA-update,dhruvvyas90/RIOT,Ell-i/RIOT,dailab/RIOT,AnonMall/RIOT,lazytech-org/RIOT,luciotorre/RIOT,rajma996/RIOT,thiagohd/RIOT,ks156/RIOT,RBartz/RIOT,patkan/RIOT,Lexandro92/RIOT-CoAP,LudwigKnuepfer/RIOT,herrfz/RIOT-old,neumodisch/RIOT,binarylemon/RIOT,Lexandro92/RIOT-CoAP,malosek/RIOT,lazytech-org/RIOT,koenning/RIOT,daniel-k/RIOT,stevenj/RIOT,adrianghc/RIOT,1blankz7/RIOT,neumodisch/RIOT,marcosalm/RIOT,tfar/RIOT,locicontrols/RIOT,aeneby/RIOT,rfswarm/RIOT,ros2/ros2_embedded_riot,locicontrols/RIOT,jbeyerstedt/RIOT-OTA-update,dailab/RIOT,jhollister/RIOT,fnack/RIOT,abkam07/RIOT,kerneltask/RIOT,ant9000/RIOT,tdautc19841202/RIOT,spium/IoT-RIOT,asanka-code/RIOT,ximus/RIOT,smlng/RIOT,bartfaizoltan/RIOT,cladmi/RIOT,LudwigKnuepfer/RIOT,jfischer-phytec-iot/RIOT,OTAkeys/RIOT,yogo1212/RIOT,asanka-code/RIOT,shady33/RIOT,basilfx/RIOT,yogo1212/RIOT,FrancescoErmini/RIOT,miri64/RIOT,1blankz7/RIOT,l3nko/RIOT,kbumsik/RIOT,gbarnett/RIOT,changbiao/RIOT,rakendrathapa/RIOT,fnack/RIOT,thomaseichinger/RIOT,spium/IoT-RIOT,thomaseichinger/RIOT,ks156/RIOT,dkm/RIOT,ximus/RIOT,koenning/RIOT,gebart/RIOT,mfrey/RIOT,x3ro/RIOT,benoit-canet/RIOT,smlng/RIOT,jasonatran/RIOT,miri64/RIOT,jhollister/RIOT,sgso/RIOT,kaspar030/RIOT,jhollister/RIOT,rfswarm2/RIOT,alex1818/RIOT,rousselk/RIOT,Lotterleben/RIOT,LudwigOrtmann/RIOT,jfischer-phytec-iot/RIOT,Lexandro92/RIOT-CoAP,kerneltask/RIOT,herrfz/RIOT-old,neumodisch/RIOT,yogo1212/RIOT,kb2ma/RIOT,daniel-k/RIOT,RubikonAlpha/RIOT,RIOT-OS/RIOT,emmanuelsearch/RIOT,Ell-i/RIOT,Osblouf/RIOT,avmelnikoff/RIOT,automote/RIOT,gbarnett/RIOT,plushvoxel/RIOT,jhollister/RIOT,latsku/RIOT,fnack/RIOT,herrfz/RIOT-old,miri64/RIOT,ximus/RIOT,MarkXYang/RIOT,centurysys/RIOT,benoit-canet/RIOT,thiagohd/RIOT,josephnoir/RIOT,Lexandro92/RIOT-CoAP,lazytech-org/RIOT,JensErdmann/RIOT,immesys/RiSyn,kushalsingh007/RIOT,RBartz/RIOT,x3ro/RIOT,bartfaizoltan/RIOT,RubikonAlpha/RIOT,shady33/RIOT,jasonatran/RIOT,thomaseichinger/RIOT,bartfaizoltan/RIOT,Ell-i/RIOT,adrianghc/RIOT,LudwigKnuepfer/RIOT,1blankz7/RIOT,smlng/RIOT,haoyangyu/RIOT,luciotorre/RIOT,Yonezawa-T2/RIOT,centurysys/RIOT,Josar/RIOT,kaleb-himes/RIOT,wentaoshang/RIOT,koenning/RIOT,jfischer-phytec-iot/RIOT,smlng/RIOT,daniel-k/RIOT,phiros/RIOT,rfuentess/RIOT,khhhh/RIOT,basilfx/RIOT,kerneltask/RIOT,lebrush/RIOT,sumanpanchal/RIOT,BytesGalore/PetersRIOT,jhollister/RIOT,binarylemon/RIOT,khhhh/RIOT,BytesGalore/RIOT,marcosalm/RIOT,tdautc19841202/RIOT,jremmert-phytec-iot/RIOT,msolters/RIOT,mtausig/RIOT,daniel-k/RIOT,daniel-k/RIOT,OlegHahm/RIOT,jferreir/RIOT,koenning/RIOT,phiros/RIOT,ros2/ros2_embedded_riot,neumodisch/RIOT,abp719/RIOT,adjih/RIOT,BytesGalore/PetersRIOT,watr-li/RIOT,patkan/RIOT,backenklee/RIOT,shady33/RIOT,DipSwitch/RIOT,l3nko/RIOT,phiros/RIOT,automote/RIOT,rakendrathapa/RIOT,mtausig/RIOT,DipSwitch/RIOT,gautric/RIOT,herrfz/RIOT,asanka-code/RIOT,ros2/ros2_embedded_riot,FrancescoErmini/RIOT,RIOT-OS/RIOT,msolters/RIOT,rakendrathapa/RIOT,Osblouf/RIOT,biboc/RIOT,luciotorre/RIOT,Josar/RIOT,toonst/RIOT,backenklee/RIOT,gebart/RIOT,rfswarm2/RIOT,BytesGalore/PetersRIOT,beurdouche/RIOT,chris-wood/RIOT,dailab/RIOT,alex1818/RIOT,RubikonAlpha/RIOT,ros2/ros2_embedded_riot,kaspar030/RIOT,A-Paul/RIOT,jhollister/RIOT,automote/RIOT,kaleb-himes/RIOT,A-Paul/RIOT,ThanhVic/RIOT,asanka-code/RIOT,A-Paul/RIOT,beurdouche/RIOT,alex1818/RIOT,asanka-code/RIOT,l3nko/RIOT,malosek/RIOT,jasonatran/RIOT,lebrush/RIOT,mtausig/RIOT,openkosmosorg/RIOT,ximus/RIOT,marcosalm/RIOT,biboc/RIOT,haoyangyu/RIOT,gbarnett/RIOT,BytesGalore/PetersRIOT,RBartz/RIOT,BytesGalore/PetersRIOT,ant9000/RIOT,emmanuelsearch/RIOT,shady33/RIOT,LudwigKnuepfer/RIOT,Darredevil/RIOT,nsol-nmsu/RIOT,RBartz/RIOT,BytesGalore/PetersRIOT,ThanhVic/RIOT,immesys/RiSyn,Lotterleben/RIOT,Yonezawa-T2/RIOT,sumanpanchal/RIOT,herrfz/RIOT-old,toonst/RIOT,EmuxEvans/RIOT,brettswann/RIOT,herrfz/RIOT,x3ro/RIOT,syin2/RIOT,emmanuelsearch/RIOT,JensErdmann/RIOT,lebrush/RIOT,LudwigOrtmann/RIOT,tfar/RIOT,spium/IoT-RIOT,koenning/RIOT,authmillenon/RIOT,wentaoshang/RIOT,RubikonAlpha/RIOT,rfswarm/RIOT,kushalsingh007/RIOT,MonsterCode8000/RIOT,rousselk/RIOT,Osblouf/RIOT,Lotterleben/RIOT,Lexandro92/RIOT-CoAP,binarylemon/RIOT,thiagohd/RIOT,dkm/RIOT,mfrey/RIOT,Lotterleben/RIOT,locicontrols/RIOT,mfrey/RIOT,jfischer-phytec-iot/RIOT,msolters/RIOT,wentaoshang/RIOT,dailab/RIOT,rakendrathapa/RIOT,backenklee/RIOT,MohmadAyman/RIOT,kushalsingh007/RIOT,MonsterCode8000/RIOT,katezilla/RIOT,A-Paul/RIOT,luciotorre/RIOT,beurdouche/RIOT,FrancescoErmini/RIOT,Lotterleben/RIOT,wentaoshang/RIOT,hamilton-mote/RIOT-OS,alex1818/RIOT,lazytech-org/RIOT,kerneltask/RIOT,aeneby/RIOT,tfar/RIOT,x3ro/RIOT,gautric/RIOT,latsku/RIOT,TobiasFredersdorf/RIOT,EmuxEvans/RIOT,tdautc19841202/RIOT,cladmi/RIOT,ros2/ros2_embedded_riot,malosek/RIOT,josephnoir/RIOT,toonst/RIOT,adrianghc/RIOT,khhhh/RIOT,chris-wood/RIOT,RIOT-OS/RIOT,khhhh/RIOT,MohmadAyman/RIOT,biboc/RIOT,OlegHahm/RIOT,lebrush/RIOT,LudwigOrtmann/RIOT,RBartz/RIOT,mziegert/RIOT,kerneltask/RIOT,cladmi/RIOT,syin2/RIOT,adrianghc/RIOT,kb2ma/RIOT,dkm/RIOT,LudwigOrtmann/RIOT,mfrey/RIOT,TobiasFredersdorf/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,AnonMall/RIOT,jremmert-phytec-iot/RIOT,biboc/RIOT,gebart/RIOT,neiljay/RIOT,immesys/RiSyn,nsol-nmsu/RIOT,arvindpdmn/RIOT,FrancescoErmini/RIOT,kbumsik/RIOT,lazytech-org/RIOT,ant9000/RIOT,marcosalm/RIOT,phiros/RIOT,adjih/RIOT,centurysys/RIOT,nsol-nmsu/RIOT,biboc/RIOT,brettswann/RIOT,herrfz/RIOT-old,malosek/RIOT,abkam07/RIOT,changbiao/RIOT,gautric/RIOT,robixnai/RIOT,openkosmosorg/RIOT,gebart/RIOT,ntrtrung/RIOT,rfswarm2/RIOT,zhuoshuguo/RIOT,chris-wood/RIOT,neiljay/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,lebrush/RIOT,aeneby/RIOT,nsol-nmsu/RIOT,openkosmosorg/RIOT,rousselk/RIOT,malosek/RIOT,thiagohd/RIOT,kYc0o/RIOT,MohmadAyman/RIOT,abp719/RIOT,l3nko/RIOT,roberthartung/RIOT,msolters/RIOT,ntrtrung/RIOT,thiagohd/RIOT,robixnai/RIOT,binarylemon/RIOT,neumodisch/RIOT,spium/IoT-RIOT,rajma996/RIOT,adjih/RIOT,kb2ma/RIOT,josephnoir/RIOT,ntrtrung/RIOT,automote/RIOT,EmuxEvans/RIOT,kaleb-himes/RIOT,attdona/RIOT,avmelnikoff/RIOT,Hyungsin/RIOT-OS,zhuoshuguo/RIOT,Josar/RIOT,1blankz7/RIOT,robixnai/RIOT,d00616/RIOT,attdona/RIOT,marcosalm/RIOT,gbarnett/RIOT,altairpearl/RIOT,changbiao/RIOT,MonsterCode8000/RIOT,1blankz7/RIOT,d00616/RIOT,rousselk/RIOT,LudwigOrtmann/RIOT,jbeyerstedt/RIOT-OTA-update,avmelnikoff/RIOT,alignan/RIOT,miri64/RIOT,herrfz/RIOT,emmanuelsearch/RIOT,jremmert-phytec-iot/RIOT,changbiao/RIOT,plushvoxel/RIOT,openkosmosorg/RIOT,EmuxEvans/RIOT,bartfaizoltan/RIOT,OTAkeys/RIOT,bartfaizoltan/RIOT,hamilton-mote/RIOT-OS,locicontrols/RIOT,patkan/RIOT,jferreir/RIOT,sgso/RIOT,alignan/RIOT,fnack/RIOT,jbeyerstedt/RIOT-OTA-update,d00616/RIOT,MonsterCode8000/RIOT,rfuentess/RIOT,kbumsik/RIOT,PSHIVANI/Riot-Code,herrfz/RIOT,DipSwitch/RIOT,avmelnikoff/RIOT,tfar/RIOT,MohmadAyman/RIOT,jbeyerstedt/RIOT-OTA-update,attdona/RIOT,JensErdmann/RIOT,ximus/RIOT,rfuentess/RIOT,openkosmosorg/RIOT,yogo1212/RIOT,gautric/RIOT,hamilton-mote/RIOT-OS,kYc0o/RIOT,kYc0o/RIOT,PSHIVANI/Riot-Code,mziegert/RIOT,immesys/RiSyn,ks156/RIOT,attdona/RIOT,mtausig/RIOT,authmillenon/RIOT,cladmi/RIOT,plushvoxel/RIOT,rousselk/RIOT,syin2/RIOT,DipSwitch/RIOT,Osblouf/RIOT,jasonatran/RIOT,spium/IoT-RIOT,l3nko/RIOT,BytesGalore/PetersRIOT,rfswarm/RIOT,rajma996/RIOT,ros2/ros2_embedded_riot,binarylemon/RIOT,jremmert-phytec-iot/RIOT,sgso/RIOT,locicontrols/RIOT,zhuoshuguo/RIOT,lebrush/RIOT,kaspar030/RIOT,sumanpanchal/RIOT,Josar/RIOT,mziegert/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,roberthartung/RIOT,RBartz/RIOT,adjih/RIOT,alex1818/RIOT,ant9000/RIOT,dhruvvyas90/RIOT,neiljay/RIOT,MonsterCode8000/RIOT,Lotterleben/RIOT,kYc0o/RIOT,jremmert-phytec-iot/RIOT,fnack/RIOT,dhruvvyas90/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,jferreir/RIOT,BytesGalore/RIOT,cladmi/RIOT,kaspar030/RIOT,MarkXYang/RIOT,avmelnikoff/RIOT,rfswarm/RIOT,TobiasFredersdorf/RIOT,rfswarm2/RIOT,roberthartung/RIOT,zhuoshuguo/RIOT,A-Paul/RIOT,kbumsik/RIOT,marcosalm/RIOT,sumanpanchal/RIOT,LudwigOrtmann/RIOT,abp719/RIOT,luciotorre/RIOT,kb2ma/RIOT,spium/IoT-RIOT,rfswarm/RIOT,dhruvvyas90/RIOT,altairpearl/RIOT,Yonezawa-T2/RIOT,adjih/RIOT,Lexandro92/RIOT-CoAP,ThanhVic/RIOT,RIOT-OS/RIOT,stevenj/RIOT,dkm/RIOT,attdona/RIOT,abp719/RIOT,beurdouche/RIOT,ntrtrung/RIOT,benoit-canet/RIOT,Ell-i/RIOT,smlng/RIOT,abkam07/RIOT,jremmert-phytec-iot/RIOT,katezilla/RIOT,katezilla/RIOT,Darredevil/RIOT,daniel-k/RIOT,ThanhVic/RIOT,kYc0o/RIOT,miri64/RIOT,sgso/RIOT,toonst/RIOT,josephnoir/RIOT,syin2/RIOT,zhuoshuguo/RIOT,altairpearl/RIOT,jasonatran/RIOT,BytesGalore/RIOT,watr-li/RIOT,rousselk/RIOT,Darredevil/RIOT,altairpearl/RIOT,haoyangyu/RIOT,l3nko/RIOT,herrfz/RIOT,tdautc19841202/RIOT,stevenj/RIOT,latsku/RIOT,stevenj/RIOT,Yonezawa-T2/RIOT,altairpearl/RIOT,latsku/RIOT,sgso/RIOT,d00616/RIOT,kaleb-himes/RIOT,wentaoshang/RIOT,benoit-canet/RIOT,tdautc19841202/RIOT,abkam07/RIOT,toonst/RIOT,Hyungsin/RIOT-OS,kb2ma/RIOT,FrancescoErmini/RIOT,sumanpanchal/RIOT,watr-li/RIOT,alex1818/RIOT,adrianghc/RIOT,Yonezawa-T2/RIOT,kushalsingh007/RIOT,mziegert/RIOT,alignan/RIOT,watr-li/RIOT,jfischer-phytec-iot/RIOT,arvindpdmn/RIOT,authmillenon/RIOT,OTAkeys/RIOT,tfar/RIOT,mziegert/RIOT,haoyangyu/RIOT,OTAkeys/RIOT,ros2/ros2_embedded_riot,Hyungsin/RIOT-OS,aeneby/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,basilfx/RIOT,jferreir/RIOT,rfswarm2/RIOT,MonsterCode8000/RIOT,latsku/RIOT,kushalsingh007/RIOT,brettswann/RIOT,robixnai/RIOT,openkosmosorg/RIOT,kbumsik/RIOT,ks156/RIOT,dailab/RIOT,centurysys/RIOT,BytesGalore/RIOT,khhhh/RIOT,aeneby/RIOT,changbiao/RIOT,d00616/RIOT,centurysys/RIOT,JensErdmann/RIOT,rfuentess/RIOT,JensErdmann/RIOT,neiljay/RIOT,Osblouf/RIOT,abp719/RIOT,ntrtrung/RIOT,OlegHahm/RIOT,fnack/RIOT,hamilton-mote/RIOT-OS,AnonMall/RIOT,abp719/RIOT,benoit-canet/RIOT,plushvoxel/RIOT,stevenj/RIOT,shady33/RIOT,MarkXYang/RIOT,MohmadAyman/RIOT,robixnai/RIOT,rajma996/RIOT,brettswann/RIOT,dhruvvyas90/RIOT,emmanuelsearch/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,patkan/RIOT,authmillenon/RIOT,1blankz7/RIOT,abkam07/RIOT,FrancescoErmini/RIOT,AnonMall/RIOT,patkan/RIOT,OlegHahm/RIOT,msolters/RIOT,changbiao/RIOT,backenklee/RIOT,RubikonAlpha/RIOT,hamilton-mote/RIOT-OS,chris-wood/RIOT,TobiasFredersdorf/RIOT,luciotorre/RIOT,tdautc19841202/RIOT,abkam07/RIOT,MarkXYang/RIOT,yogo1212/RIOT,Lotterleben/RIOT,bartfaizoltan/RIOT