Merge pull request #14 from m14t/master

Change debugging echo's to error_log()s
Update README.md with SMTP support information.
Update symfony config, thanks @adipasquale. Closes #15
First pass at composer.json
Allow user defined debug logging. Closes #11

You can now set a callable with Swift_AWSTransport::setDebug and it will
use that as the debug logging method.