Add initial implementation of docs for API coverage info

I added a couple missing doc pages (for YARA and generic test mechanisms.)

I've setup an initial page that can be used to indicate API coverage of important STIX constructs/modules.

Notes:
- I listed constructs as `partial` if any fields within that construct OR any fields within sub-constructs are not yet implemented.
- I listed `STIX Features: Relationships` as `partial` because I'm not sure if `every.possible.relationship` is covered
- I split the coverage info into a few separate tables to make it easier to navigate
- This information is all based off of the current profile xslx in the `profile` branch
constructs