Adds support for URLs with embedded credentials

I usually use my GitHub username as part of my origin URL, so as to avoid constantly typing it. e.g. ```http://boenrobot@github.com/boenrobot/myRepo.git```.

Sometimes I even consider adding my password (but then I remember I'd be writing it in plain, clearly visible, text...).

This plugin is great, except that it doesn't support this. This pull request adds this ability to the GitHub strategy.


__NOTE: I HAVE NOT TESTED THIS, AT ALL.__

If it works, it should be a no brainer to add it to the other strategies as well.

Alternatively, maybe you could use java.net.URL instead of regex, and get the scheme, host and path that way?