individuated versioning of annotation types

[keighrim]

This PR emancipates versions of individual annotation types from the big MMIF version, letting them have their own version bump only when a change explicitly added to a type. The rationale has already been discussed for a long time in #14 and https://github.com/clamsproject/mmif-python/issues/163 . In short, the PR will add automatic version number generation for each annotation types defined in clams.vocabulary.yaml during build.py. Specifically,

• at_type versions are automatically inferred by "diff"ing clams.vocabulary.yaml of cwd and that from the latest git tag
• at_type versioning scheme is simply a single integer
• when rendered on a web page, nothing is appended
• the inferred at_type versions are stored as a JSON file next to the hierarchy index.html file, so that it can be used in
  1. next MMIF release cycle
  2. mmif-python SDK

(moved discussion points to the underlying issue card)

[keighrim]

All recent discussion points are resolved with new commits. Should be ready to merge (or a full review, if needed)

[keighrim]

It's been open for over two week, and I haven't heard about any problem. Lots of SDK issues are blocked by this, so I'll proceed and merge this.