Added HTML5 DOM parser library to add experimental support for HTML5
Added support for an optional HTML5 parser.  It can be enabled by setting the following environment variable in the .htaccess file:
RewriteRule .* - [E=USE_HTML5_PARSER:1,E=USE_CONSERVATIVE_CACHING:0]
(Note that also added flag to disable conservative caching.
Todo:  Add section about this in the manual.

The HTML5 Parser was necessary to parse some complex HTML5 documents.  The flag to disable conservative caching improves performance dramatically on sites that are meant to be public.