Remove eventmachine

I don't think this library currently needs EventMachine at all. Calling `EM.defer` in effect just calls `Thread.new` with a wad of overhead. 

We might want to spawn a few threads that each call store message, but I don't currently understand enough to make that call.

I've spent a couple of hours reading about how threads work in Ruby. I've posted some thoughts on Flowdock and I highly recommend this article series: http://www.jstorimer.com/blogs/workingwithcode/8085491-nobody-understands-the-gil

@mmmmmrob, @malcyL - thoughts?