Added email archiving option to IMAP transport
Minor alterations to @yellowcap's pull request submission:

* Using a query parameter argument (rather than the entire query string)
  to specify the folder into which e-mail messages should be archived.
* Duplicating the IMAP tests; this could probably be a bit more simply
  done, but we'll at least be verifying both archived and non-archived
  use cases.
* Simplifying some aspects of the documentation to include references
  to this new feature.
Bumping version number to 3.3.
Create archive folder if it does not exist.