fd.o #27878: glib-ginterface-gen: output gtk-doc separately
fd.o #27878: glib-ginterface-gen: output gtk-doc separately

gtk-doc will happily document all .h files, so we don't need the
doc-comments to be in the same files as the declarations or
implementations.

Also, ensure that output is in UTF-8.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib