[EME] spec updates published

Highlights from the last week:

   - Removed the second needkey event (19788).
   - Require key IDs (19810)
   - Updated examples to use asynchronous XHR and addEventListener (16541,
   18928).
   - Added Issue blocks for error codes and asynchronous loading of the CDM.
   - Swapped 5.1 <-> 5.2 then 4 <-> 5.
   - Removed the FAQ, which was superfluous and diverging from the main
   text.