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 logic behind this is such: you either send the email successfully, or there is some error that prevents it to be sent. The request type here is an email, not an SMTP command. Which of the many replies SMTP server sent during the mail session should be chosen to represent success in this case? Furthermore, even if you take 250 reply when mail data is accepted, it's still the only one to be expected in case of success, so is there any point in keeping that information?