[Pixman] Project moved to github

[Adam Jackson]

Well that was quick. The project page is over here now:

https://gitlab.freedesktop.org/pixman/pixman

New git URLs:

https://gitlab.freedesktop.org/pixman/pixman.git
git at gitlab.freedesktop.org:pixman/pixman.git

Bugzilla issues were imported. I'll make a pass through the patchwork
queue (it's not long) to migrate anything that looks worth preserving.
If you'd like to be added as a developer just give a shout.

- ajax