Honour pod encoding

This patchset replaces the utility functions which run raw POD through  decode_utf8 and then strip out POD markup using regexes.  The replacement code honours the =encoding declaration (if present) and strips out POD markup by rendering to plain text using Pod::Simple::Text.

There are two known differences in behaviour with the new strip_pod() routine:
1. `L<link|http://www.google.com>`, now renders as `link <http://www.google.com>` rather than `link`
2. `L<Module/section>` now renders as `"section" in Module foo` rather than `section in Module foo`

If the previous behaviour of either item is deemed preferable or any other changes need rework, then let me know.

With these patches in place, it should be possible to upgrade Pod::Simple to 3.22 which will allow improved rendering of non-ASCII POD source that lacks an =encoding declaration.  An earlier attempt to upgrade POD::Simple caused the indexer to fail on B/BO/BOOK/Acme-MetaSyntactic-Themes-1.009.tar.gz - I've confirmed that this distribution can now be indexed.