[evol] set the 'micalg' parameter in signed mails
[evol] sign outgoing mails, and lot's of fixes and code improvement in mail handling (related to signing, crypting, and preparing/chaining the two)
[evol] handle incoming encrypted messages
[fix] remove logger usage in tmail extension
[evol] properly moved tmail signature handling out of postman in a library (which i should probably suggest upstream)