Fix test failure on VMS.

Patch from Craig A. Berry.
Don't emit __top href unless there is alo a TOC (index).
Be more consistent in creating XHTML IDs.
Die on multiple settings of pull parser source.
Timestamp v3.20.
Increment to v3.20.
Fix some typos.
Whine on first non-ASCII byte-sequence and use it to guess Latin-1 vs UTF-8
Don't turn on codes_in_verbatim by default for the XHTML formatter
Better advice on how to override handle_text in subclass

Need to invoke the base version of handle_text for proper
escaping and handling of accept_targets_as_html.
Replace the "not-totally-brilliant wrapping algorithm" with Text::Wrap
Join subsequent text segments before passing them to _handle_text

This makes it much easier to process text using custom handlers.
Introduce handle_code method
Merge pull request #26 from grantm/encoding-warnings

Whine on first non-ASCII byte-sequence and use it to guess Latin1 vs UTF8
Note Grant McLean's contributions.
Merge pull request #27 from gisle/codes_in_verbatim

Don't turn on codes_in_verbatim by default for the XHTML formatter
Note "codes_in_verbatime" change in XHTML.
Merge pull request #28 from gisle/handle_code

Add handle_code as overrideable method on Pod::Simple::XHTML
Adjust new corpus lines for new line wrapping.
Note changes from Gisle.