Switch from setup.py to pyproject.toml

[WhyNotHugo]

Motivation and Context

This'll make configuring a few tools a bit easier. The previous approach is kinda of deprecated anyway.

How Has This Been Tested?

CI is about to do some more testing. But basically:

mkvirtualenv tmp
pip install -e .

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #170 (a891b20) into master (8ebdfe8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #170   +/-   ##
=======================================
  Coverage   92.62%   92.62%           
=======================================
  Files          16       16           
  Lines         746      746           
  Branches       50       50           
=======================================
  Hits          691      691           
  Misses         45       45           
  Partials       10       10           

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[blag]

LGTM. Once this is merged let's add an issue to cleanup dev dependencies a bit. Some of them appear to be out of date, or are no longer required.

[blag]

Still needed?