quick toc at top of docs, free up horizontal space

Proposed changes per my message here: http://news.php.net/php.webmaster/14786

* Quick toc is displayed horizontally at top of the page, and becomes fixed once the user scrolls passed it.
* The "current section" (based on scroll position) is distinguished as the user scrolls.
* Removed some of the right-padding to free up more screen real estate.

I would still prefer fluid 100% width, but that's a more dramatic change and looks a little strange with the logo/navigation/search being in the center. Perhaps all the header content could be left-aligned? (As old fashioned as that sounds.)