make clean before zstd-lz4 compatibility tests

to ensure zstd is rebuilt with lz4 support

Merge pull request facebook#859 from terrelln/31

Prepare for ZSTD_WINDOWLOG_MAX == 31

Merge pull request facebook#808 from facebook/dev

Zstandard v1.3.1

Merge pull request facebook#750 from facebook/dev

fixed wrong assert() condition

Merge pull request facebook#686 from facebook/dev

v1.2.0

Merge branch 'dev'

Merge pull request facebook#531 from facebook/dev

Zstandard v1.1.3

updated manual

minor display improvement in fuzzer when nb of tests is very large

updated NEWS