Rmail to mail initial work

This is a work in progress to get the train moving for RMail to Mail migration, there are lots of bits around that are RMail specific which needs to be updated. This PR also includes several other fixes which should be split out and merged first:

- syck to psych
- remove iconv
- fix_encoding in util.rb (without iconv it works kind of like Decoder in heliotrope)

migration is based on suggestions by @rakoo in #22.

Related issues: #22, #23, #17.