Fails to build with setuptools >= 61.0.0

[stratakis]

With the latest setuptools porcupine fails to build with:

/usr/bin/python3 setup.py build
error: Multiple top-level packages discovered in a flat-layout: ['share', 'install'].
To avoid accidental inclusion of unwanted files or directories,
setuptools will not proceed with this build.
If you are trying to create a single distribution with multiple packages
on purpose, you should not rely on automatic discovery.
Instead, consider the following options:
1. set up custom discovery (`find` directive with `include` or `exclude`)
2. use a `src-layout`
3. explicitly set `py_modules` or `packages` with a list of names
To find more information, look for "package discovery" on setuptools docs.

A probable fix would be to add either py_modules=[] or packages=[] to setup.py

See also https://github.com/pypa/setuptools/issues/3197#issuecomment-1078770109