Added `app/views/arbre` as autoload path when using Rails.
Added tag DSL methods
Added one more spec.
Added AJAX rendering to Arbre::Rails::LegacyDocument.
Bug fix

* Bug fix: classes specified in the class definition are not overwritten anymore by those passed to the
  `build!` method.
Change in attribute processing.
Bug fix: querying using multiple selectors now works.
Bug fix in Rails rendering.
Adding public RSpec API.
Version bump to 2.0.1.