Adding ssh protocol support to "github-protocols".

Adding SSH support for "GitHub". This fixes a few issues I've ran into and provides another method to try when everything else fails.  (https fails because of auth in "git clone", and git being disabled in "github" configuration)

This is based on:
- https://help.github.com/articles/generating-ssh-keys
- http://git-scm.com/book/ch4-1.html#The-SSH-Protocol