- Test Mark4 8, 16, 64 track modes
- Test all Mark5B modes
- Test seeking
- Add Mark5CB sync word
- Implement validate
- Make test suite

* Implement more decoders
  x Mark4
  x Mark5B
  ? Mark5CB -- compatibility mode
    - still need sync word
  - Mark5C
* Documenation
  x For developers
  x For users
x Implement seek
  x mark5_stream function
  - Test it!
x Test all 64 track VLBA modes
x File Stream -- minimum file size
x mark5_stream_open compatibility function