v1.0.0

• using libzim 7.x
• Python 3.9 support
• [breaking] Using new libzim 7-based API for both reader and writer
  • No more namespaces
  • Defaulting to zstd compression
  • https://github.com/openzim/libzim/blob/master/ChangeLog
• Rewrote all tests for new API ; using libzim's own test ZIM files to test reader
• Code-coverage now includes Cython code as well
• macOS releases are signed and notarized
• Early-failure on invalid destination ZIM path