GSoC: finagle-smtp - initial

This is initial version of SMTP client for Finagle, which I am working on during GSoC'14.
For now it supports sending independent commands to SMTP server and sending a simple text email to one ore more addresses (without cc, bcc and reply-to). Usage is described in `README.md`. 
I'm not sure you need to show multiple ways of handling failure here (although it certainly doesn't hurt!). My question was more about the fact that you know `res` has succeeded if you get to this point—you've either handled the errors in the preceding `onFailure` or you've blown up with a `MatchError`.