Docs: cleaned up Tasks pages: clarified its purpose and reorganized
Docs: cleaned up Tasks pages: clarified its purpose and reorganized

jaceklaskowski/sbt,xeno-by/old-scalameta-sbt,xeno-by/old-scalameta-sbt,xuwei-k/xsbt,dyx/sbt,jkinkead/sbt,twitter-forks/sbt,xuwei-k/xsbt,mdedetrich/sbt,corespring/sbt,Duhemm/sbt,xeno-by/old-scalameta-sbt,twitter-forks/sbt,xuwei-k/xsbt,pdalpra/sbt,jaceklaskowski/sbt,Duhemm/compiler-bridge,sbt/sbt,mdedetrich/sbt,jaceklaskowski/sbt,som-snytt/xsbt,sbt/sbt,dyx/sbt,sbt/sbt,Sciss/sbt,jkinkead/sbt,Duhemm/sbt,xuwei-k/xsbt,dyx/sbt,twitter-forks/sbt,jkinkead/sbt,xeno-by/old-scalameta-sbt,mdedetrich/sbt,dansanduleac/sbt,mdedetrich/sbt,sbt/sbt,adriaanm/sbt,mdedetrich/sbt,xeno-by/old-scalameta-sbt,sbt/sbt,mdedetrich/sbt,jaceklaskowski/sbt,sbt/sbt,jkinkead/sbt,twitter-forks/sbt,jaceklaskowski/sbt,mdedetrich/sbt,sbt/sbt,jkinkead/sbt,twitter-forks/sbt,xeno-by/old-scalameta-sbt,dyx/sbt,dyx/sbt,pocketberserker/sbt,jasonchaffee/sbt,xuwei-k/xsbt