New attr_initializable plugin for Rails
README, licence file and gemspec updates and new Travis-CI configuration

* Renames README.rdoc to README.md and adds Travis-CI badges
* Renames MIT-LICENSE to LICENSE and fixes up name
* Fixes up gemspec
* Adds Travis-CI configuration file
* Updates dummy app's database configuration to support Travis-CI
New Manufacturer and Widget models
Define Mixins::InitializableAttributes inline for time being