Big email 3.0 API changes, with updated unit tests and documentation.

Big email 3.0 API changes, with updated unit tests and documentation.
Briefly (from the NEWS file):

- Updates for the email package:
  + All deprecated APIs that in email 2.x issued warnings have been removed:
    _encoder argument to the MIMEText constructor, Message.add_payload(),
    Utils.dump_address_pair(), Utils.decode(), Utils.encode()
  + New deprecations: Generator.__call__(), Message.get_type(),
    Message.get_main_type(), Message.get_subtype(), the 'strict' argument to
    the Parser constructor.  These will be removed in email 3.1.
  + Support for Python earlier than 2.3 has been removed (see PEP 291).
  + All defect classes have been renamed to end in 'Defect'.
  + Some FeedParser fixes; also a MultipartInvariantViolationDefect will be
    added to messages that claim to be multipart but really aren't.
  + Updates to documentation.