v4.16.0

• Improve the base URI behavior when resolving a $ref to a resolution URI
  which is different from the resolved schema's declared $id.
• Accessing jsonschema.draftN_format_checker is deprecated. Instead, if you
  want access to the format checker itself, it is exposed as
  jsonschema.validators.DraftNValidator.FORMAT_CHECKER on any
  jsonschema.protocols.Validator.

Full Changelog: v4.15.0...v4.16.0