Fixups to the GMail pop3 unit tests
Fixed logic bug in MemMove implementation

Fixes issue #23 and issue #58
Work around another GMail IMAP bug (returns a NIL envelope for embedded messages)

Fixes issue #59
Added async methods for IMailFolder so ImapFolder now has async versions of everything
Implemented a better workaround for a GMail IMAP bug

Fixes issue #59 (thanks to Anton Gordienko)
Modified MemMove to no-op if src == dest or length == 0
Bumped version to 0.19.0.0
Added missing xml docs