support skipping DontCall and Model constants in ruby 1.9+
Refactor our helpers and add tests.

In order to test Sinatra helpers, you have to create a module. Sinatra
uses anonymous modules when you use the shorthand helpers method, which
makes testability almost impossible. This breaks out helpers into
multiple modules and adds appropriate testing.
Merge pull request #58 from optopus/feature/helper-tests

Feature/helper tests