While `pip3 install .` still works, `python3 setup.py install` does not (and
ditto for Python2), because subpackages of `pygments` don't get installed. Even
running `find_packages` on its own has consistent behavior:

```
$ python3
>>> from setuptools import setup, find_packages
>>> find_packages(exclude=['tests'])
['pygments', 'pygments.filters', 'pygments.lexers', 'pygments.formatters', 'pygments.styles']
>>> find_packages(include=['pygments'])
['pygments']
```

The bug seems to have been introduced in
8d0828bbfc5b8deb7525a19e1037704f644563da.

Tested on macOS 10.14 with Homebrew Python 2.7.17 and 3.7.5.

The tests package is found as a package due to presence of __init__.py. Use include to ensure only pygments gets installed.

On modern Python installations, setuptools should always be available
and should always be preferred. Can remove the fallback to distutils.

Replace the pygmentize script with a __main__.py in the package.

Document support for Python 3.8 (released October 14th, 2019) and PyPy
and add them to the test matrix.

The long description failed to parse due to whitespace issues.