doc: atomic: provide explanation about why atomic_int_t is struct
doc: atomic: provide explanation about why atomic_int_t is struct

See also https://github.com/RIOT-OS/RIOT/pull/2321#issuecomment-72088818

mfrey/RIOT,thomaseichinger/RIOT,beurdouche/RIOT,TobiasFredersdorf/RIOT,kaspar030/RIOT,roberthartung/RIOT,asanka-code/RIOT,adjih/RIOT,rakendrathapa/RIOT,MohmadAyman/RIOT,RIOT-OS/RIOT,ks156/RIOT,cladmi/RIOT,MohmadAyman/RIOT,wentaoshang/RIOT,tfar/RIOT,backenklee/RIOT,aeneby/RIOT,basilfx/RIOT,jasonatran/RIOT,d00616/RIOT,ant9000/RIOT,Hyungsin/RIOT-OS,RIOT-OS/RIOT,toonst/RIOT,dkm/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,kerneltask/RIOT,jasonatran/RIOT,Josar/RIOT,x3ro/RIOT,neiljay/RIOT,attdona/RIOT,attdona/RIOT,hamilton-mote/RIOT-OS,MohmadAyman/RIOT,syin2/RIOT,alignan/RIOT,Ell-i/RIOT,adrianghc/RIOT,cladmi/RIOT,jremmert-phytec-iot/RIOT,rousselk/RIOT,yogo1212/RIOT,wentaoshang/RIOT,roberthartung/RIOT,basilfx/RIOT,rousselk/RIOT,tfar/RIOT,yogo1212/RIOT,OTAkeys/RIOT,attdona/RIOT,OTAkeys/RIOT,katezilla/RIOT,cladmi/RIOT,jbeyerstedt/RIOT-OTA-update,dailab/RIOT,OlegHahm/RIOT,gebart/RIOT,shady33/RIOT,altairpearl/RIOT,kbumsik/RIOT,shady33/RIOT,immesys/RiSyn,Yonezawa-T2/RIOT,Yonezawa-T2/RIOT,x3ro/RIOT,FrancescoErmini/RIOT,A-Paul/RIOT,toonst/RIOT,RIOT-OS/RIOT,adjih/RIOT,kaspar030/RIOT,TobiasFredersdorf/RIOT,rfuentess/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,neiljay/RIOT,jbeyerstedt/RIOT-OTA-update,adjih/RIOT,x3ro/RIOT,dailab/RIOT,jremmert-phytec-iot/RIOT,katezilla/RIOT,A-Paul/RIOT,katezilla/RIOT,Ell-i/RIOT,d00616/RIOT,kerneltask/RIOT,kYc0o/RIOT,neiljay/RIOT,immesys/RiSyn,rousselk/RIOT,biboc/RIOT,rfuentess/RIOT,malosek/RIOT,adrianghc/RIOT,immesys/RiSyn,roberthartung/RIOT,kaspar030/RIOT,Hyungsin/RIOT-OS,BytesGalore/RIOT,roberthartung/RIOT,jremmert-phytec-iot/RIOT,jremmert-phytec-iot/RIOT,malosek/RIOT,rakendrathapa/RIOT,dailab/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,MohmadAyman/RIOT,avmelnikoff/RIOT,dailab/RIOT,attdona/RIOT,syin2/RIOT,hamilton-mote/RIOT-OS,jfischer-phytec-iot/RIOT,Hyungsin/RIOT-OS,zhuoshuguo/RIOT,ant9000/RIOT,Josar/RIOT,plushvoxel/RIOT,BytesGalore/RIOT,LudwigKnuepfer/RIOT,rfuentess/RIOT,dailab/RIOT,OlegHahm/RIOT,asanka-code/RIOT,FrancescoErmini/RIOT,toonst/RIOT,adrianghc/RIOT,LudwigKnuepfer/RIOT,asanka-code/RIOT,brettswann/RIOT,thomaseichinger/RIOT,adrianghc/RIOT,neumodisch/RIOT,jasonatran/RIOT,ks156/RIOT,yogo1212/RIOT,miri64/RIOT,zhuoshuguo/RIOT,shady33/RIOT,gautric/RIOT,authmillenon/RIOT,jbeyerstedt/RIOT-OTA-update,biboc/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,gebart/RIOT,TobiasFredersdorf/RIOT,Yonezawa-T2/RIOT,biboc/RIOT,shady33/RIOT,immesys/RiSyn,neumodisch/RIOT,thomaseichinger/RIOT,basilfx/RIOT,d00616/RIOT,d00616/RIOT,Hyungsin/RIOT-OS,RIOT-OS/RIOT,kerneltask/RIOT,OTAkeys/RIOT,jfischer-phytec-iot/RIOT,asanka-code/RIOT,basilfx/RIOT,josephnoir/RIOT,kaspar030/RIOT,jfischer-phytec-iot/RIOT,kYc0o/RIOT,Yonezawa-T2/RIOT,hamilton-mote/RIOT-OS,dkm/RIOT,katezilla/RIOT,backenklee/RIOT,mtausig/RIOT,gautric/RIOT,Yonezawa-T2/RIOT,BytesGalore/RIOT,kaleb-himes/RIOT,avmelnikoff/RIOT,kYc0o/RIOT,Hyungsin/RIOT-OS,plushvoxel/RIOT,rakendrathapa/RIOT,asanka-code/RIOT,neumodisch/RIOT,miri64/RIOT,cladmi/RIOT,x3ro/RIOT,neiljay/RIOT,dkm/RIOT,zhuoshuguo/RIOT,A-Paul/RIOT,hamilton-mote/RIOT-OS,gautric/RIOT,wentaoshang/RIOT,neiljay/RIOT,jasonatran/RIOT,altairpearl/RIOT,backenklee/RIOT,rajma996/RIOT,gautric/RIOT,smlng/RIOT,kaleb-himes/RIOT,tfar/RIOT,ks156/RIOT,thomaseichinger/RIOT,mfrey/RIOT,rakendrathapa/RIOT,kaspar030/RIOT,kaleb-himes/RIOT,adjih/RIOT,authmillenon/RIOT,yogo1212/RIOT,brettswann/RIOT,altairpearl/RIOT,LudwigOrtmann/RIOT,zhuoshuguo/RIOT,kb2ma/RIOT,shady33/RIOT,Josar/RIOT,mfrey/RIOT,toonst/RIOT,wentaoshang/RIOT,gebart/RIOT,ks156/RIOT,jremmert-phytec-iot/RIOT,malosek/RIOT,BytesGalore/RIOT,alignan/RIOT,beurdouche/RIOT,A-Paul/RIOT,rajma996/RIOT,mtausig/RIOT,plushvoxel/RIOT,aeneby/RIOT,rajma996/RIOT,cladmi/RIOT,lazytech-org/RIOT,jfischer-phytec-iot/RIOT,alignan/RIOT,biboc/RIOT,kbumsik/RIOT,yogo1212/RIOT,mfrey/RIOT,rajma996/RIOT,avmelnikoff/RIOT,OTAkeys/RIOT,kb2ma/RIOT,FrancescoErmini/RIOT,OlegHahm/RIOT,brettswann/RIOT,d00616/RIOT,d00616/RIOT,LudwigKnuepfer/RIOT,jbeyerstedt/RIOT-OTA-update,plushvoxel/RIOT,Josar/RIOT,jfischer-phytec-iot/RIOT,smlng/RIOT,thomaseichinger/RIOT,TobiasFredersdorf/RIOT,shady33/RIOT,miri64/RIOT,mtausig/RIOT,rfuentess/RIOT,zhuoshuguo/RIOT,malosek/RIOT,rajma996/RIOT,lazytech-org/RIOT,josephnoir/RIOT,miri64/RIOT,Ell-i/RIOT,brettswann/RIOT,OTAkeys/RIOT,LudwigKnuepfer/RIOT,alignan/RIOT,kb2ma/RIOT,ks156/RIOT,rakendrathapa/RIOT,beurdouche/RIOT,aeneby/RIOT,syin2/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,adrianghc/RIOT,gebart/RIOT,miri64/RIOT,rousselk/RIOT,wentaoshang/RIOT,Josar/RIOT,smlng/RIOT,brettswann/RIOT,beurdouche/RIOT,authmillenon/RIOT,josephnoir/RIOT,neumodisch/RIOT,kbumsik/RIOT,lazytech-org/RIOT,adjih/RIOT,ant9000/RIOT,LudwigOrtmann/RIOT,neumodisch/RIOT,LudwigOrtmann/RIOT,altairpearl/RIOT,Yonezawa-T2/RIOT,lazytech-org/RIOT,immesys/RiSyn,malosek/RIOT,LudwigKnuepfer/RIOT,rousselk/RIOT,LudwigOrtmann/RIOT,kerneltask/RIOT,kb2ma/RIOT,authmillenon/RIOT,lazytech-org/RIOT,RIOT-OS/RIOT,TobiasFredersdorf/RIOT,basilfx/RIOT,malosek/RIOT,rajma996/RIOT,FrancescoErmini/RIOT,LudwigOrtmann/RIOT,zhuoshuguo/RIOT,tfar/RIOT,BytesGalore/RIOT,brettswann/RIOT,ant9000/RIOT,wentaoshang/RIOT,Ell-i/RIOT,avmelnikoff/RIOT,aeneby/RIOT,beurdouche/RIOT,mtausig/RIOT,syin2/RIOT,smlng/RIOT,OlegHahm/RIOT,kerneltask/RIOT,attdona/RIOT,kYc0o/RIOT,A-Paul/RIOT,dkm/RIOT,attdona/RIOT,toonst/RIOT,kbumsik/RIOT,immesys/RiSyn,katezilla/RIOT,mfrey/RIOT,FrancescoErmini/RIOT,syin2/RIOT,aeneby/RIOT,alignan/RIOT,tfar/RIOT,asanka-code/RIOT,plushvoxel/RIOT,mtausig/RIOT,backenklee/RIOT,avmelnikoff/RIOT,rousselk/RIOT,gebart/RIOT,gautric/RIOT,authmillenon/RIOT,josephnoir/RIOT,kb2ma/RIOT,altairpearl/RIOT,MohmadAyman/RIOT,roberthartung/RIOT,kYc0o/RIOT,kbumsik/RIOT,FrancescoErmini/RIOT,jremmert-phytec-iot/RIOT,Ell-i/RIOT,neumodisch/RIOT,dkm/RIOT,smlng/RIOT,LudwigOrtmann/RIOT,hamilton-mote/RIOT-OS,altairpearl/RIOT,x3ro/RIOT,rfuentess/RIOT,rakendrathapa/RIOT,OlegHahm/RIOT,josephnoir/RIOT,MohmadAyman/RIOT,jasonatran/RIOT,jbeyerstedt/RIOT-OTA-update,ant9000/RIOT,kaleb-himes/RIOT,backenklee/RIOT,kaleb-himes/RIOT,yogo1212/RIOT,biboc/RIOT,authmillenon/RIOT