Add Bundler and Foreman

I've added support for Bundler and Foreman.

Bundler will allow us to declare our Ruby dependencies in the `Gemfile` - in this case, I've declared `github-pages` and `compass`.

Foreman will allow us to start up the development process through a single command - which will run both applications inside the same terminal window. I've defined `jekyll build` and `compass watch` inside the `Procfile`.