Several improvements on docs.
Added SMTP exceptions to return error responses.
Docs for errors module.
Minor typos and edits on docs.
Improved docs about errors module.
Added test case for errors module.
TestCase for __init__ module.
Test case for testing module.
Unused code.
Improved coverage for __init__ module.
Minor edit on docs.
Blank lines raises a UnrecognisedCommand exception.
A exception on request callback must to response as an Internal confusion.
Docs for new manipulation of request callbacks.
Tests for SMTPError with log_message.
Improved index doc, added logo.