* Introduce a new "added-in" template and use it on endpoints
* Use "added-in" on schema properties too
* Annotate sections of the spec with their added versions
* Demo of "added-in" on a room version (to be fleshed out)
* Use clearer versioning semantics
* Update and fix validator for Swagger custom properties
* Fix docs
* Cut/paste room version spec to its own page
* Move grammar to bottom + add feature matrix
The version grammar is not as interesting as the actual room versions, so this moves that whole section to the bottom.
* Fix all links to room versions
