Changes from 2.7.1 to 2.8.0

• New bytedelta filter added. SIMD support for Intel and ARM platforms is there.
  We have blogged about this: https://www.blosc.org/posts/bytedelta-enhance-compression-toolset.rst
  Thanks to Aras Pranckevičius for inspiration and initial implementation.

• Minor improvements in BloscLZ, leading to better compression ratios in general.
  BLoscLZ version bumped to 2.5.2.

• Updated internal zlib-ng to 2.0.7.

• Used const qualifier where possible in b2nd. Thanks to @cf-natali.