[CIVIS-1835] VER v1.16.0 release

[jacksonlee-civis]

v1.16.0 is happening!

• [x] (For Civis employees only) Reference to a relevant ticket in the pull request title
• [x] Changelog entry added to CHANGELOG.md at the repo's root level
• [x] Description of change in the pull request description
• [x] The CircleCI builds have all passed

[jacksonlee-civis]

@madopal Since I don't cut releases in an afternoon, I won't be cutting a new civis-python v1.16.0 release until tomorrow morning (2021-12-14).

Also, I've verified that this new v1.16.0 version would be compatible with a corresponding civis-python version bump in the datascience-python Docker image (the image would build successfully, as the CI build has verified). See https://github.com/civisanalytics/datascience-python/pull/84 , and in particular this commit to test things out:

https://github.com/civisanalytics/datascience-python/pull/84/commits/2abee883b71b09a87de8a79b5e7d4ebe25c124b2