[I18n-sig] Support for "wide" Unicode characters

[Martin v. Loewis]

> IMO, unicode(), u.encode() and the \U notation should all use
> 'strict' ...  and perhaps the exception messages produced by the
> narrow build could be marketing-aligned and point the punter to the
> wide build.

Both unicode and u.encode support an optional errors parameter, for
which Guido proposed to accept an additional value of "lenient". The
default is "strict".

Regards,
Martin