Add support for structured arguments in :mod:`imaplib` command methods.  A
*message_set* and lists of flags or other atoms can now be passed as
sequences instead of preformatted strings, and the
:meth:`~imaplib.IMAP4.search`, :meth:`~imaplib.IMAP4.fetch`,
:meth:`~imaplib.IMAP4.sort`, :meth:`~imaplib.IMAP4.thread` and
:meth:`~imaplib.IMAP4.uid` methods accept a *params* keyword argument that
substitutes and quotes ``?`` placeholders.
