Idomatic Ruby instead of Shell

The built in Ruby methods for deletion seem a little cleaner here. I'm fairly sure that this is a system independent implementation as well.

**update:** I added a commit that uses FileUtils::mkdir_p. I removed the `dir =` assignments since those variables aren't being used. Honestly, if they are being used as documentation, I don't think they are adding any clarity. The imperative `mkdir` seems a lot more expressive in and of itself than `dir`. But If you would like to keep them, just let me know and I'll modify my commit.