Switch to fully pyproject.tml-based build

[jayqi]

This PR switches us to a fully pyproject.toml-based build.

We were previously partially using a PEP 517 build using setuptools for pip installs, but still using the deprecated setup.py commands for building wheels and sdist.

This PR additionally migrates our project metadata from setup.py to pyproject.toml (PEP 621).

Build backend and dynamic versioning

We were previously using setuptools as a build backend and versioneer for dynamic versioning from git.

I tried 3 different backend setups that would maintain this functionality:

• setuptools + versioneer
• setuptools + setuptools_scm
• pdm-pep517

I found that pdm-pep517 worked the best with the sanest defaults and required the least configuration.

Versioneer does support declaring Versioneer's tool configuration in pyproject.toml, but unfortunately Versioneer still seems to require having a setup.py. I got a runtime error that setup.py was missing when trying to refresh our Versioneer setup with the latest version of Versioneer.

setuptools_scm is another package that provides dynamic versioning from git, and is used as an example in setuptools' docs for doing so. The dynamic versioning part worked fine. Unfortunately, a side effect is that there isn't a way to turn off setuptools_scm's other feature which is to automatically include all files tracked by git in the build. It was difficult and annoying to have to then wrangle MANIFEST.in to exclude all of these files.

We may also consider getting rid of the dynamic versioning functionality, but I didn't want to take on that decision in this PR. The main benefit that it provides right now is that the version string we label the post-save initialization code with will be distinguishable between development versions of nbautoexport vs releases.

[codecov-commenter]

Codecov Report

Merging #113 (b50724c) into master (3a06119) will increase coverage by 0.0%.
The diff coverage is 100.0%.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #113   +/-   ##
======================================
  Coverage    98.5%   98.5%           
======================================
  Files           8       8           
  Lines         425     427    +2     
======================================
+ Hits          419     421    +2     
  Misses          6       6           

Impacted Files	Coverage Δ
nbautoexport/utils.py	100.0% <100.0%> (ø)

[github-actions]

🚀 Deployed on https://deploy-preview-113--zen-roentgen-1e5a72.netlify.app

[ejm714]

This is so much simpler! Thanks for taking this on @jayqi

Two small questions, neither of which is blocking