Additional handling for HTML wrappers

Hi Jess,

Just made a couple small tweaks to add more modular handling of DB->HTMLBook conversion:

* Added an $include-html-wrapper param, which lets you choose whether or not to wrap the HTML content in the standard `<html>/<head>/<body>` tagging. This is on by default, but off so that you can generate bits of an HTML document and then combine as needed.

* Turned off inclusion of the XML declaration at top of document to make the combining mentioned in previous bullet easier to do.

Thanks,
Sanders