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`. 
Ok, I've created a new branch. Here are [the changes](https://github.com/suncelesta/finagle/commit/6a7c6afeb4b66081f510b7d14a922bc35d90d6eb) for you to review.