Sync with PyTables' hdf5-blosc2 source

[ivilata]

Since this project has been "adopted" by the Blosc organization, and since the version of this code vendored in PyTables was also evolved by people related with Blosc, it may make sense to sync both code bases by:

1. Updating this repo with the latest source in PyTables' hdf5-blosc2 (this is what this issue is for).
2. Replacing PyTables' hdf5-blosc2 with a submodule pointing to this repo, as was suggested for hdf5-blosc in Convert HDF5-Blosc sources into Git submodule PyTables/PyTables#1197 (this would be a future issue in the PyTables project).

Thanks!