The directory structure of the input web site now controls directory the layout of the
doc hierarchy. This simplifies authoring documents and enriches the UI we generate.
This also fixes the broken link problem with the GitHub staging sites. Most links work
now.
Our sitemap.xml now contains all that it should, and excludes stuff that it shouldn't contain.
* Update about page and landing page.
* Update about page to use markdown instead of html, fix ordering of about page and presentation to match other pages.
Also fixed a few more places where the old tagline was around, all have the new tagline now.