Merge pull request #4 from kitop/master

Make it Rails 4 compatible
Bump to 2.1.0

* Relax rspec dependency
* Add rake dependency
Refactor some internals

* Get rid of the call to eval
* Use URL-style connection string instead of options hash
* Inline VERSION constant
* Sqelch bundler warning
* Bump to 3.0.0
Bump to 3.0.1
Inline version string
Assign primary key to new models

Looks like somewhere in Rails 3 the primary key for a model
became configurable and stopped defaulting to id.