gl3n goes github

[David]

It's done, I moved gl3n (http://dav1dde.github.com/gl3n/) over to 
github: https://github.com/Dav1dde/gl3n

One of the reasons why I moved gl3n was issue #1 
https://bitbucket.org/dav1d/gl3n/issue/1/github-mirror - nearly every D 
project is at github (also gdc moved), so it was also time to move.

I will keep the old bitbucket repo for a while, but I won't update it, 
same with the docs at bitbucket.