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 inteded `UnspecifiedReply` to be a 'protoreply', not classified yet, which is formed during decoding, and `Reply` to be a supertype for all final reply classes. Since final replies have the same characteristics as a protoreply, except they are classified, I made `Reply` a suptype of `UnspecifiedReply`.
I will talk with my mentors on this matter and try to resolve such issues.