major refactoring...

* **Sections are now called Areas:**  This is is because it was becoming
  difficult to name the different parts of the navigation hierarchy. So
  now it is simply: Area -> Module/Namespace -> Section -> Item
  In the case of the api "area" you have, for example
  api (Area) -> ngRoute (Module) -> directive (Section) -> ngView (Item)

* **Landing Pages:** Since we have a folder hierarchy in terms of the paths
  to pages, e.g. `api/ng/directive/ngClick` we need to have a page to render
  if you go directly to each of the containing folders, e.g.
  `api`, `api/ng` and `api/directive`.  The landing-pages processor now
  creates such pages if no doc already exist for them.  The navigation
  hierarchy and bread crumbs also make use of this feature by providing
  anchors to these landing pages at the relevant places.