• Updated jsonschema dependency version, removed deprecated refResolver
  (@ostefano)
• Enforce requirement that network-traffic.http-request-ext.request_header is a
  list of strings instead of a singular string
• Allow -ext extensions in SDOs
• Fixed bug when loading files containing unicode characters on certain
  platforms
• Fixed bug with duplicate log entries when importing the validator script as a
  library (@ostefano)
• Switched to including IETF data as package data instead of pulling and
  caching locally, removed caching options, and removed requests-cache and
  appdirs dependencies (@vEpiphyte)
• Dropped support for Python 3.7