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`. 
The success replies to different commands usually have different informational strings, so for each command there is actually a specific success reply. Not all of them even have the same reply code. However, the email can be sent only if all the commands succeed. (Here, if one of the recepients is not accepted, the session is aborted, and the error pertained to that recipient is returned; for more flexibility there is Smtp client).