Add description of each of the keyword arguments to BaseField.__init__(), adds description for choices too.
Add description of each of the keyword arguments to BaseField.__init__(), adds description for choices too.

MakerReduxCorp/mongoengine,ContextLogic/mongoengine,nicolascine/mongoengine,KarimAllah/mongoengine,closeio/mongoengine,MongoEngine/mongoengine,noirbizarre/mongoengine,elephanter/mongoengine,ConsumerPhysics/mongoengine,WingGao/mongoengine,ms5/mongoengine,RussellLuo/mongoengine,starsirius/mongoengine,reallistic/mongoengine,gmacon/mongoengine,sourcelair/mongoengine,prijindal/mongoengine,Catstyle/mongoengine,MRigal/mongoengine,khallaghi/mongoengine,cogniteev/mongoengine,MakerReduxCorp/mongoengine,eli-b/mongoengine,hmarr/mongoengine,losintikfos/mongoengine,muhammad-ammar/mongoengine,jimmyshen/mongoengine,nathanial/mongoengine,yarneo/mongoengine,blaggacao/mongoengine,touilleMan/mongoengine,Multiposting/mongoengine,larsbutler/mongoengine,alex/mongoengine,cogniteev/mongoengine,ProgressivePlanning/mongoengine,conversocial/mongoengine,DavidBord/mongoengine,Davidrjx/mongoengine,ContextLogic/mongoengine,gavincabbage/mongoengine,aszwemin/mongoengine,iandd0824/mongoengine,Davidrjx/mongoengine,newvem/mongoengine,depop/mongoengine-stripped,colinhowe/mongoengine,9nix00/mongoengine