Add wrappers for rails html5 helpers

* added #casein_week_field
* added #casein_date_field
* added #casein_url_field
* added #casein_search_field
* added #casein_telephone_field
* added #casein_range_field
* added #casein_datetime_field
* added #casein_time_field
* added #casein_month_field
* added #casein_datetime_local_field
* added #casein_email_field
* added #casein_number_field
* added #casein_color_field
* added TestModel to rails_test_app and used it for testing these new field types
* cleaned up some missed checkins from the initial rails_test_app commit
* updated .gitignore to skip files in rails_test_app
* moved casein_helper_spec to casein/ subdir to match the app layout
* updated README

Note: this PR is built on top of the Bundler/Rspec branch so if that branch gets merged, it should reduce the size of the diff since this diff is compared against the current master (as of 12/20/2014)