Add `passthrough` type.
Add `passthrough` type.

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