Fixes issues with the Gem (paths and missing bits).

This fixes a couple of problems which show up with Ruby 2.1 with paths and also adds in a few other parts common to a gem (Rakefile, etc).

This also:

* Switches the `test` to `spec` to follow the syntax used.
* Adds a `Rakefile` to help with the gem and tests.
* Adds a version file and moves it out of the `gemspec`.