Building and testing Gtk3 on Windows with Appveyor

[Zakariyya Mughal <zaki mughal gmail com>]

Hello,

I just wanted to share some recent work I did to build the Gtk3 Perl
module using a MinGW64 GTK+ 3 package provided through MSYS2.

I've automated the installation so that it can be built on the Appveyor
continuous integration service in order to test my application on
Windows.

Here is a write up of what I had to go through at
<https://project-renard.github.io/doc/development/meeting-log/posts/2016/05/03/windows-build-with-msys2/>.

I'd love to work on packaging this up in a way that it can be used for
distribution to end-users.

Cheers,
- Zaki Mughal