This reverts commit b578d2febfd35f80fcfa1ce1bdf18d44d21b1581.

Cleanly separates tests from the package itself. Prevents the tests
being installed to site-packages. Tests are still distributed with the
source distribution by MANIFEST.in.

Avoids installing tests in production environments, leading to less
total code in the environment.

Allows running static analysis (lint/flake8) separately from testing the
library. Reduces the redundant times static analysis runs. Previously
ran after every test environment, but only needs to run once, requiring
less tests resources.

For lint, use "skip_install = True" as installing psutil isn't required
to do static analysis. For details on this configuration, see:

https://tox.readthedocs.io/en/latest/config.html#confval-skip_install=BOOL

> skip_install=BOOL
>
> Do not install the current package. This can be used when you need the
> virtualenv management but do not want to install the current package
> into that environment.

No "test" directory exists. The configuration is unneeded.

Support for Python 3.3 was dropped in version 5.4.1. Support for Python
3.2 was dropped earlier. Remove all references to these unsupported
versions including documentation, scripts, workarounds, etc. Eases
maintenance as fewer workarounds are used for unsupported environments.