Replace Setup.py With Pyproject.toml and Ensure Correct spdx-tools Dependency Specified

[jspeed-meyers]

The current setup.py resulted in a recent hiccup for spdx-online-tools: spdx/spdx-online-tools#418

[jspeed-meyers]

While investigating this, I discovered that setup.py files are no longer the recommended way to do Python packaging.

See https://setuptools.pypa.io/en/latest/userguide/quickstart.html#setup-py

Instead, pyproject.toml is recommended.

Additionally, this pyproject.toml file should indeed include spdx-tools.

So here's the task for a future PR:

• Remove setup.py
• Replace with a pyproject.toml
• Ensure that pyproject.toml includes the spdx-tools dependency

The pyproject.toml should be something like this:

[project]
name = "ntia-conformance-checker"
version = "0.0.2"
dependencies = [
    "spdx-tools>=0.7.0rc0",
]

The pyproject.toml file will also need to specify where the package is.