Support for Github gists

Created gist version using https://github.com/defunkt/gist gem since that was closest in spirit to Armando's existing script (specifically authentication method using ENV variables) and also defaults to public gists, although delete not supported.  There is a more up to date gem for gists using oauth and supporting more functionality https://github.com/ConradIrwin/jist/blob/master/lib/jist.rb However that would require more work to integrate.  Would like to create some user stories, cucumber scenarios before further work here :-)

The update approach could in principle be changed since github supports editing of gists while maintaining the same URL, so no need to create new ones for each update?  

Hacked this up as not much time (family all sick with flu), ideally would have test harness around everything ... cucumber features and scenarios describing and driving what the user is doing.  Would be awesome if code in files was also being checked for accuracy by being run against a test suite, e.g. placed into some rails framework to ensure that everything in the book had passed it's own tests and was working properly.

Hope this might be of use.  Github gists rock!