Add "active-support" as dependency

Include the ActiveSupport additions to String
Store currently processing action on Context
Add default localizer to configuration

Allows easy translation of failure & success messages according to the
action failing the context.
Use localizer when passing/failing the context

Delegate message lookup to the localizer itself
Updated README to show localizer usage
Localizer now accepts options to pass to I18n

Allows interpolation of messages in the localization adapter
Update succeed/fail methods to accept options hash
Updated README to support new I18n options usage
Make Localizer#translate a private method
Adds acceptance test for localization adapter
Rename Localizer => LocalizationAdapter

Like this class and setting name much better, since we really are
providing an adapter layer.
Remove I18n deprecation warning in spec suite
DRYing up the LocalizationAdapter logic
Using the old Ruby hash syntax, cleaning up namespaces