When attempting to base64-decode a payload of invalid length (1 mod 4),
properly recognize and handle it.  The given data will be returned as-is,
i.e. not decoded, along with a new defect, InvalidBase64LengthDefect.

Fix typos found by codespell in docs, docstrings, and comments.

Correctly handle addresses whose username is an empty quoted string.

* Fix multiple typos in code comments

* Add spacing in comments (test_logging.py, test_math.py)

* Fix spaces at the beginning of comments in test_logging.py

The original algorithm tried to delegate the folding to the tokens so
that those tokens whose folding rules differed could specify the
differences.  However, this resulted in a lot of duplicated code because
most of the rules were the same.

The new algorithm moves all folding logic into a set of functions
external to the token classes, but puts the information about which
tokens can be folded in which ways on the tokens...with the exception of
mime-parameters, which are a special case (which was not even
implemented in the old folder).

This algorithm can still probably be improved and hopefully simplified
somewhat.

Note that some of the test expectations are changed.  I believe the
changes are toward more desirable and consistent behavior: in general
when (re) folding a line the canonical version of the tokens is
generated, rather than preserving errors or extra whitespace.

in regular expressions.

While there is not real bug in this case, using re.IGNORECASE without re.ASCII
leads unexpected behavior.
Instead of adding re.ASCII, this commit removes re.IGNORECASE flag because
it's easier and simpler.

This commit removes dead copy of the pattern in email.util module too.
While the pattern is same, it is compiled separately because it had different flags.

Leading whitespace was incorrectly dropped during folding of certain lines in the _header_value_parser's folding algorithm.  This makes the whitespace handling code consistent.

If max_line_length=None is specified while using the Compat32 policy,
it is no longer ignored.

* Replaced list(<generator expression>) with list comprehension
* Replaced dict(<generator expression>) with dict comprehension
* Replaced set(<list literal>) with set literal
* Replaced builtin func(<list comprehension>) with func(<generator
  expression>) when supported (e.g. any(), all(), tuple(), min(), &
  max())

This is a further restoration of backward compatibility, as well as
being correct per the RFCs.

It turns out we can't depend on email.message getting imported every place
message_factory is needed, so to avoid a circular import we need to special
case Policy.message_factory=None in the parser instead of using monkey
patching.  I had a feeling that was a bad idea when I did it.

This is buggy in the old email code as well, but it doesn't affect anything
there because only the default line length is ever used there.

Patch by Claude Paroz.

Original patch by Martin Panter, new policy fixes by me.

And most of the tools.

Patch by Emanual Barry, reviewed by me, Serhiy Storchaka, and
Martin Panter.

This is a wholesale reorganization and editing of the email documentation to
make the new API the standard one, and the old API the 'legacy' one.  The
default is still the compat32 policy, for backward compatibility.  We will
change that eventually.

Patch by Berker Peksag.

Patch by Costas.

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.

This affects documentation, code comments, and a debugging messages.

Patch from Dmitry Shachnev.

email.utils.make_msgid() to strengthen the uniqueness of the message ID.