v1.4.0

Added

• The WebVTT-related box definitions by TrueDread were pulled over to the main repository.

Changed

• Replaced Setuptools with Poetry for a better dependency management experience.

Fixed

• Fixed multiple issues with the TrackEncryptionBox definition,
  • version must now be 0 or 1.
  • _reserved1 key has been replaced with its actual definition of default byte block information.
  • is_encrypted must now be 0 or 1.
  • iv_size must now be 0, 8, or 16.
• Fixed the test_tenc_parse test.
• All tests now successfully complete again on Python 3.9 and older. They fail on 3.10 and newer due to breaking
  changes in Python breaking compatibility with construct 2.8.8. Newer versions of construct break fundamentals
  of pymp4. See #23.