Eliminate install-dependency from 'setuptools'

[amdei]

There is a fragment in setup.py:
https://github.com/jazzband/prettytable/blob/master/setup.py#L29

install_requires=["setuptools", "wcwidth"],

Does setuptools really necessary here?
Its presence make it difficult to convert prettytable to, for example, deb-package using fpm tool (https://github.com/jordansissel/fpm) - resulted package depends on setuptools too, what, I believe, isn't really necessary.

[hugovk]

Yes, it's needed to be able to get the version number using pkg_resources: #66

But this could be replaced with importlib.metadata, in the stdlib from 3.8 and has a backport too:
https://github.com/pypa/setuptools_scm#retrieving-package-version-at-runtime

Would you like to put together a PR? Thanks!

[hugovk]

Please see PR #96.