Support enabling via `pyproject.toml`

[WilliamJamieson]

This should allow the setting of the use_extension_helpers option in the pyproject.toml file using:

[tool.extension-helpers]
use_extension_helpers = true

in addition to the already supported option of doing this in the setup.cfg file.

Fixes #47

[WilliamJamieson]

Do we really need to support python 3.7? I'll remove my walrus...

[codecov[bot]]

Codecov Report

Merging #48 (8e0c854) into main (5bb1895) will decrease coverage by 3.10%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
- Coverage   79.86%   76.77%   -3.10%     
==========================================
  Files           4        4              
  Lines         298      310      +12     
==========================================
  Hits          238      238              
- Misses         60       72      +12     

Impacted Files	Coverage Δ
extension_helpers/__init__.py	24.00% <0.00%> (-22.16%)	:arrow_down:

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[WilliamJamieson]

The py36 job should probably be dropped see issue #49

[WilliamJamieson]

I don't think the py38-test-linuxgcc-conda and py39-downstream CI failures are related. Looks like something has changed since the last time they were run.

[WilliamJamieson]

@astrofrog I added tomli as a requirement in 29be02d; however, I can easily make it an optional requirement say extension-helpers[toml] or something? Let me know what you prefer.

[larrybradley]

It would be nice to get this in a new extension-helpers release. Why has this PR stalled?

@astrofrog, @WilliamJamieson - Are changes need beyond a rebase on https://github.com/astropy/extension-helpers/pull/50 ?

[WilliamJamieson]

I forgot all about this. I'll see if I can fix it on Monday.