ci: use cibuildwheel

[mayeut]

As discussed in #41, rework CI to use cibuildwheel & GHA.

I will split in multiple PRs & update this list accordingly:

• Use same convert_to_generic_platform_wheel script as cmake: 104b0ca
  Prepare for universal2, allow to create py2.py3 wheels
  Available in standalone PR chore: use same convert_to_generic_platform_wheel.py script as cmake #49
• repair_wheel.py script: 0f23004
  Create py2.py3 wheels, ensures delocate/auditwheel are used on macOS/Linux to check the wheels.
• Update requirements: f2e0802
  Multiple requirements allow to install only what's needed for a given stage.
• use cibuildwheel: e31875a
  Use cibuildwheel to build wheels, move everything to GHA, remove CircleCI, AppVeyor, TravisCI & scikitci

GHA workflow can be seen on my fork

pre-requisite: #49

[mayeut]

converted to draft, let's try to split this a bit for easier reviews.

[mayeut]

@henryiii, @jcfr,

I'll merge this one in about 8 hours if you have no objections by then.
It's very similar to what's been done on CMake and will allow to move forward scikitci, travisci, ... having issues right now. I will try to enhance this once this gets merged similar to what @henryiii has done on CMake.