[Vala] valac can read a typelib in place of a vapi binding

[Adam Dingle <adam yorba org>]

I realized to my surprise today that valac (0.11.7) can read a GObject 
introspection type library in place of a VAPI file!  For example, I can 
specify '--pkg PeasGtk-1.0' on the command line and valac will read 
types from /usr/lib/girepository-1.0/PeasGtk-1.0.typelib, which lets me 
use libpeas types even though there is no libpeas.vapi anywhere.

1. Is this documented somewhere?  How long has this cool feature existed 
without my knowing about it?  :)

2. Is there a long-term plan to deprecate .vapi files in favor of type 
libraries?  Can type libraries express everything that .vapi files can?

adam