Proof of concept: refactor astropy-helpers into extension-helpers

[astrofrog]

This is a companion PR to astropy/astropy#9726 and APE 17 and demonstrates how we can remove most of the functionality into astropy-helpers, keeping only utilities related to compiling C and Cython extensions. The remaining functionality is:

• The machinery to auto-detect Cython files and define extensions
• The framework for collecting extensions defined in setup_package.py files
• The OpenMP helpers

This also renames astropy-helpers to extension-helpers to reflect its new purpose and the fact it is very general and can be used beyond the project. This should not be merged at this point and is up to easily be able to visualize the changes that would be required.

For experimenting purposes, I have uploaded an alpha release to PyPI: https://pypi.org/project/extension-helpers/

[codecov]

Codecov Report

Merging #503 into master will decrease coverage by 11.41%.
The diff coverage is 48.41%.

@@             Coverage Diff             @@
##           master     #503       +/-   ##
===========================================
- Coverage   41.37%   29.96%   -11.42%     
===========================================
  Files          19        9       -10     
  Lines        1670      534     -1136     
===========================================
- Hits          691      160      -531     
+ Misses        979      374      -605

Impacted Files	Coverage Δ
extension_helpers/tests/test_openmp_helpers.py	0% <ø> (ø)
extension_helpers/openmp_helpers.py	0% <ø> (ø)
extension_helpers/tests/__init__.py	0% <0%> (ø)
extension_helpers/conftest.py	0% <0%> (ø)
extension_helpers/tests/test_setup_helpers.py	0% <0%> (ø)
extension_helpers/utils.py	70.51% <100%> (ø)
extension_helpers/setup_helpers.py	64.7% <64.7%> (ø)
extension_helpers/distutils_helpers.py	83.87% <83.87%> (ø)
extension_helpers/__init__.py	92.85% <92.85%> (ø)
... and 4 more

---

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[pllim]

+694 −5,678 -- me likey!

Do you also plan to rename the repo?

[pllim]

Or maybe this really should be a new repo? If you insist to have this here, should at least branch out the "old way" in case others need to patch it for one reason or another.

[bsipocz]

The "old-way" is already been branched out into 2.0.x, 3.y.x, 4.0.x etc branches.

[astrofrog]

Closing as this branch has now been pushed to https://github.com/astropy/extension-helpers