Release 1.12.0

In order to avoid problems with platforms with incomplete development
library codecs, the default is now to compile the internal codecs.
Users can still compile Blosc with external codecs by properly setting
cmake options like PREFER_EXTERNAL_SNAPPY, PREFER_EXTERNAL_ZLIB or
PREFER_EXTERNAL_ZSTD.

Also, the internal Zstd codec has been updated to 1.3.0.

For more info, please see the release notes in:

https://github.com/Blosc/c-blosc/blob/master/RELEASE_NOTES.rst