Fix template missing errors

By default the haml gem doesn't seem to handle setting itself up as
a template provider for rails 3. Adding the haml-rails gem sets this
up by default and also provides the rails generators for the views.
Fix failing config spec

Was failing with following error. Assuming this was a typo.

  1) Configuration of a site valid configuration is a valid site
     Failure/Error: sa
     NameError:
       undefined local variable or method `sa' for #<RSpec::ExampleGroups::ConfigurationOfASite::ValidConfiguration:0x007fe898fe8e08>
     # ./spec/features/config_spec.rb:27:in `block (3 levels) in <top (required)>'
Add haml-rails to Gemfile

haml-rails was not being required from the gemspec. Not sure if this is
the right way to fix this issue.
Merge pull request #24 from amcoder/fix-template

Fix template missing errors