Using Bundler, rcov -> simplecov, deprecated requires

Using Bundler [1] to manage installed gems for the project.

RCov does not support Ruby 1.9.X. The RCov github page suggests using
SimpleCov [2] instead.

There were also a couple or `require` statements in the Rakefile
that were causing problems (errors, etc) after new gem versions and the
like.

[1] http://gembundler.com
[2] https://github.com/colszowka/simplecov