zstandard: vendor python-zstandard 0.11
The upstream source distribution from PyPI was extracted. Unwanted
files were removed.
The clang-format ignore list was updated to reflect the new source
of files.
The project contains a vendored copy of zstandard 1.3.8. The old
version was 1.3.6. This should result in some minor performance wins.
test-check-py3-compat.t was updated to reflect now-passing tests on
Python 3.8.
Some HTTP tests were updated to reflect new zstd compression output.
# no-check-commit because 3rd party code has different style guidelines
Differential Revision: https://phab.mercurial-scm.org/D6199