Implemented support for turbolinks, when it's present.

To enable it, just place it in the Gemfile of your application:

```ruby
gem 'jquery-turbolinks'
gem 'turbolinks'
```

Bugs that need fixing include: some tests fail

This does _not_ place a dependency on turbolinks, it has to be in the Gemfile!
Cool, want to add to the PR? I'm a bit tied up at present