DKIM signing prototype
Working DKIM signing implementation
Add notes about DKIM to README
mimemail's encode_headers now return list with one element per header.

This was needed for DKIM signing of headers, containing ";". Also,
minor performance improevement, because of no '++' operations.
Relaxed DKIM canonicalization method for headers implemented
Fix tests (broken after relaxd/simple become default)
Add support for 't' and 'x' DKIM tags; improeved QP encoding for tag values
Merge pull request #57 from seriyps/just-dkim

DKIM signing for outgoing emails, cleaned-up