Authoring section (#252)

* Expand authoring section. Change attr-map-* to attr-mapml-viewer-*.

* Update Authoring examples to include local and remote content

* Remove trailing commas to get rid of IDE visual noise

* Add link rel=icon to replace default m4h cg icon in specification

* Update "Contexts in which this element can be used:" sections for all 
elements re: local / remote content

* Update  and move diagram of coordinate systems into 'Semantics' section. 

* Remove duplicate and almost empty Authoring section (was 5.3)