Python 3.9 support

[JanczarKurek]

Hi,

Currently if you try running under python3.9 you will get a stack dump looking like this:

Traceback (most recent call last):
  File "/usr/lib64/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib64/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/janczarknurek/.cache/bazel/_bazel_janczarknurek/8ef58595ad1884d5f3dbc0914d9c6141/external/com_apt_itude_rules_pip/tools/create_pip_repository.par/__main__.py", line 33, in <module>
    main()
  File "/home/janczarknurek/.cache/bazel/_bazel_janczarknurek/8ef58595ad1884d5f3dbc0914d9c6141/external/com_apt_itude_rules_pip/tools/create_pip_repository.par/__main__.py", line 13, in main
    wheels.download(args.repository_directory, args.requirements, *extra_args)
  File "/tmp/tmp4hxy_fue/com_apt_itude_rules_pip/src/piprules/wheels.py", line 18, in download
    with _add_pip_import_paths_to_pythonpath():
  File "/usr/lib64/python3.9/contextlib.py", line 117, in __enter__
    return next(self.gen)
  File "/tmp/tmp4hxy_fue/com_apt_itude_rules_pip/src/piprules/wheels.py", line 31, in _add_pip_import_paths_to_pythonpath
    import setuptools
  File "/tmp/tmp4hxy_fue/pip_setuptools/setuptools/__init__.py", line 16, in <module>
    from setuptools.dist import Distribution, Feature
  File "/tmp/tmp4hxy_fue/pip_setuptools/setuptools/dist.py", line 24, in <module>
    from setuptools.depends import Require
  File "/tmp/tmp4hxy_fue/pip_setuptools/setuptools/depends.py", line 7, in <module>
    from .py33compat import Bytecode
  File "/tmp/tmp4hxy_fue/pip_setuptools/setuptools/py33compat.py", line 55, in <module>
    unescape = getattr(html, 'unescape', html_parser.HTMLParser().unescape)
AttributeError: 'HTMLParser' object has no attribute 'unescape'

If i understand correctly - this has to do with the version of setuptools the project is using. Setuptools in version < 44 does not support python3.9. This should be updated to allow user to use python3.9.