Continued proposed refactoring

* Deprecate verb in AS 2.0 in favor of @type approach
* Start providing clearer AS 1.0 to AS 2.0 processing rules
* New AS1->AS2 specific JSON-LD @context
* Strengthen extension MUST IGNORE language, mention JSON constructs
that cannot be used within JSON-LD, provide examples for the known
GeoJSON incompatibility,
* Adding in the application/stream+json media type registration (this
was never formally registered before)