Rewrite to use ScreenOrientation interface (closes #13)

* added ScreenOrientation interface
* Rewrote examples
* Removed redundant "dependencies"
* Merged dependencies and terminology section
* Made Promise linkable in dependencies
* Moved ScreenOrientation and Extension to navigator object to the top
of the document
* Removed "concepts" section (left all inner content, of course)
* rewrote how to get attributes
* removed redundancy when invoking lock() and unlock()
* Moved enums to their  own sections (it was annoying trying to find
them. Now the show up in the TOC!)
* Introduced "security condition" concept. This fixes the weird
dependency on the FULLSCREEN API. That's now moved to the "Interaction
with the FullScreen API" section
*  Added Interaction with FullScreen API section. Defined what to do
when full screen fully exits there.
* moved conformance section to bottom of document
Updated it to this:

```HTML
          The <code><dfn id=
          "widl-ScreenOrientation-onchange">onchange</dfn></code> attribute is
          an <a>event handler</a> whose corresponding <a>event handler event type</a> 
          is <code>change</code>.
```

That matches what Anne's spec has, includes the name of the event handler event type, without having to repeat the information that is already in the WebIDL.