[TIDOC-1581] Add missing fields to JSCA supplied by the YAML: availability, permission and osver

To test, from the `apidoc` directory run:
~~~
./docgen.py -f jsca -o ../dist
~~~

Open the ../dist/api.jsca file and check to see the `availability` and `permission` fields are added to the properties, and for API elements that specify the `osver` in the YAML, those values are populated in the JSCA file in the `userAgents` field.