Bugfix: Options were not propagated down to subschemas.
Bugfix: Empty arrays resulted in invalid schemas because it still
  included an items property.
Bugfix: items was being set to a list even when merge_arrays was set to
  True. This resulted in overly permissive schemas because items are
  matched optionally by default.
Improvement: Positional Array Matching - In order to be more consistent
  with the way JSON Schema works, the alternate to merge_arrays is no
  longer never to merge list items, but instead to merge them based on
  their position in the list.
Improvement: Schema Incompatibility Warning - A schema incompatibility
  used to cause a fatal error with a nondescript warning. The message
  has been improved and it has been reduced to a warning.