Added ability to clone non github remotes

I love yeoman, I think it's damn good. The problem I was having was dealing with an internal git repo where I wanted to use `.remote()`. Instead of just copy and pasting remote so that it can work with _any_ archive, I updated it (and the tests) so that you can now pass it a full url to an archive, eg either will work:

`this.remote('yeoman', 'generator', 'master', cb, refresh);` or `this.remote('https://github.com/yeoman/generator/archive/master.zip', cb, refresh);`

I hope the tests pass! :cake: