Compress/Decompress routines should return Errnos

[asomers]

When an error happens, the API leaves the user wondering why. I suggest that blosc_compress, blosc2_compress_ctx, blosc_decompress, blosc2_decompress_ctx, blosc_getitem, and blosc2_getitem_ctx should all return -1 on error and set errno. Alternatively, Blosc could define its own error codes with negative values.

This would be especially useful for the decompress routines, which can return an error either because the destination buffer is too small, the data is corrupted, or the decompression library is unavailable.