Changes from 2.5.0 to 2.6.0

• [API] Now it is possible to pass filter ID to a User Defined Filter.

• Unified convention for BLOSC_SPLITMODE environment variable in Blosc
  and Blosc2. The list of valid values is "ALWAYS", "NEVER", "AUTO" and
  "FORWARD_COMPAT" now.

• Unified convention for BLOSC_SPLITMODE enum in Blosc and Blosc2 headers.