FEAT: including Graham Chiu's SMTP protocol source into repository

It is version downloaded from his repository: https://github.com/gchiu/Rebol3/blob/master/protocols/prot-smtp.r

As it was not tested yet (in this branch), I'm not including it into a build. Main reason of this commit is, that I don't want to loose track of this file as it may be useful in the future (although it will need update to support TLS)