* The choice is not what the function *returns*, but what it *does*
(raising an exception is not returning a value).
* Recommend "assert" more strongly, and additionally recommend an
error message with the assert.
* Back up that recommendation in the sample code.
* chore(changelog): add changelog for 2.1.0 release
* doc(rewind): add documentation a new feature `rewind` that can replay a cassette
* doc(exception): add documentation on the new behavior of the CannotOverwriteExistingCassetteException message