Added :publish_states_as_json method

This method returns a pseudo JSON value string.

During some UI work I needed a JSON representation
of the publish_states, so hence this method.
Reworked /lib and /spec structure
Renamed Licence
Clearing out old stuff
Updated Gemfile
Cleaned up main loader
Cleaned up .gitignore
Added Guardfile for testing
Improved Rakefile
Updated README
Improved Docs courtesy of SDoc
Ignore Gemfile.lock
Updated gemspec and version bump to 1.2.0

Versions are now following the official DatatMapper version numbers.