Changes from 2.20.0 to 2.21.0

• New public API b2nd_save_append. It is useful for appending a b2nd
  array into a file. Thanks to Barak Ugav (@barakugav) for the PR (#683).

• Added new public APIs for the shuffling filters:

  • blosc2_shuffle
  • blosc2_unshuffle
  • blosc2_bitshuffle
  • blosc2_bitunshuffle

  Thanks to Theodore Tsirpanis (@teo-tsirpanis) for the PR (#681).

• Fix a potential nullptr exception on b2nd_create_ctx with null storage.
  Thanks to Barak Ugav (@barakugav) for the PR (#684).

• The CMake dependency acquisition has been improved.
  Thanks to Theodore Tsirpanis (@teo-tsirpanis) for the PR (#682).

• Now, a blosc/config.h is generated in the binary directory. Fixes
  failures when configuring from the same source directory in parallel.
  Thanks to Theodore Tsirpanis (@teo-tsirpanis) for the PR (#679).