Adds Fivemat reporter.

This is a reporter based on @tpope's [fivemat][1]. Its like a cross between a dot reporter and a spec reporter. Not too much noise but enough info to know what is running. I find it useful when running large test suites. Here's what the output looks like, 

![Fivemat Output](http://i.imgur.com/mcvLPZF.png?1)


Usage is,

$ mocha -R fivemat

[1]: https://github.com/tpope/fivemat