Add simplified version of `filter` functionality to CLI

[benelliott]

This change allows you to use the filtering option through the CLI, with the simplifying assumption that the filter will be a case-insensitive regex.

I wanted this functionality so I could filter out things like the .git directory using the CLI wrapper and thought it would be worth sharing.

[benelliott]

Travis failure exists on master.

[davglass]

Published in cpr@2.0.1

fyi, the travis issue isn't with the code it's with the tests and it's installed via npm 3.x which screws with the directory structure that it's using :)

[benelliott]

Great, thanks!