• Parse # type: ... comments if on Python 3.8+ (jingw, #220).
• Bump minimum Python version to 3.6 (Jendrik Seipp, #218). The last
  Vulture release that supports Python 2.7 and Python 3.5 is version 1.6.
• Consider all files under test or tests directories test files
  (Jendrik Seipp).
• Ignore logging.Logger.propagate attribute (Jendrik Seipp).