Add attr to api docs.
Add attr to api docs.

lez/peewee,Dipsomaniac/peewee,zhang625272514/peewee,coreos/peewee,fuzeman/peewee,Sunzhifeng/peewee,coleifer/peewee,Dipsomaniac/peewee,coleifer/peewee,jnovinger/peewee,coleifer/peewee,Sunzhifeng/peewee,py4a/peewee,zhang625272514/peewee,Dipsomaniac/peewee,ghukill/peewee,new-xiaji/peewee,mackjoner/peewee,bopo/peewee,teserak/peewee,bopo/peewee,Sunzhifeng/peewee,new-xiaji/peewee,zhang625272514/peewee,wenxer/peewee,stas/peewee,bopo/peewee,jarrahwu/peewee,jarrahwu/peewee,coreos/peewee,fuzeman/peewee,wenxer/peewee,ronyb29/peewee,jnovinger/peewee,coreos/peewee,jarrahwu/peewee,new-xiaji/peewee,softside/peewee