Added Gtk-Doc in 3.0

[Ankit Vani]

On Tue, Feb 11, 2014 at 1:57 PM, Mark Doliner <mark at kingant.net> wrote:
> Do you know if it's possible to build the docs without compiling? (Not
> critical, but would be nice for our nightly doc generation script that
> lived at https://developer.pidgin.im/doxygen/)

Gtk-Doc introspects the libraries (libpurple, libfinch, libpidgin) for
type heirarchies, GObject properties, GSignal docs etc. So having the
libraries ready to introspect is necessary.

> Do you have plans for doc/PERL-HOWTO.dox and doc/TCL-HOWTO.dox? Maybe
> these should be converted to gtk-doc?

I will do those once I'm back home (I'm travelling right now). I left them
out for now since these loaders will be removed in the .plugins branch in
favour of GPlugin loaders.