Here there go some random thoughts for Blosc 2.0:

* Try to find a classification for the return codes and standardize
  them.  Use constants in blosc.h for naming them.

* blosc_init() should return a structure that should serve as a
  context for other calls. So instead of blosc_set_blocksize(size_t
  size), you would have blosc_set_blocksize(blosc_context* context,
  size_t size).

  See: https://github.com/Blosc/c-blosc/pull/66/files#r20010877 for
  some discussion.

* Add more space in header for allowing more compressors and filters.
  Discuss how much should that space be in the mailing list.

* Make two different versions of the header so that it supports 32-bit
  sizes as well as 64-bit?  That would allow to compress buffers larger
  than INT_MAX.