XHTML formatter 'xhtml' regions

I recently got my Advent calendar converted entirely to Pod::Simple where it
had previously used Pod::Parser.  I needed two features added.

I sent Allison and David a pull request for the first, this morning.  It allows
you to say "=head1 becomes <h2>" or "becomes <h3>" and so on, which makes it
easier to produce an HTML fragment for inclusion in a larger document.

I am unsure whether the other feature is welcome.  It makes this:

  =for xhtml <tag>...</tag>

...pass the XHTML right through.  This is invaluable for producing my colorized
code samples.  (I assume it also works as a begin/end block.)

If it is welcome, I will add it to Pod::Simple::XHTML and issue another pull
request.  If not, I will release it as a subclass.

-- 
rjbs