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
Maybe we should avoid fancy syntax and simply have:
```js
function show() {
  ...
}
```