Armature GitHub Pages based website

The purpose of this PR is to be able to host a web version of the Armatures on a GitHub Pages site.
This adds a rake task to create/update the gh-pages branch that github uses.

For the moment it builds a fully unstyled website, this can be added later.

Unfortunately, a pre-processing is needed to produce the gh-pages, so it's not possible (except by using a CI system) to update/push the gh-pages branch on every master merge.

Enjoy :)