documents: Add basic support for version 3 of the Google Documents API
documents: Add basic support for version 3 of the Google Documents API

Support for v3 of the API will replace support for v2, given that v3 is now
stable and v2 is no longer recommended.

Helps: https://bugzilla.gnome.org/show_bug.cgi?id=593537

Distrotech/libgdata,Distrotech/libgdata,pwithnall/libgdata,pwithnall/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata,Pecisk/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata-gtasks,Distrotech/libgdata,GNOME/libgdata