have github workflow generate wheel as artifact

[cielavenir]

• not building native module on platforms other than linux
  • macos CI is half-running but it is applied only when I change setup.py in order not to build native module on macos
  • for ci view I decided to keep macos unlisted (from matrix) though
• have github workflow generate wheel as artifact (Provide a wheel package? #4 will be mostly solved although you need to upload whl to pypi)
• add Python 3.9

cf (artifact) https://github.com/cielavenir/eventfd/actions/runs/635082406

[cielavenir]

@palaviv didn't know I need to add -p manylinux1 flag. fixed.

[cielavenir]

@palaviv sorry, my wheel was not conforming manylinux rule. I fixed it. sorry.

fixed wheel https://github.com/cielavenir/eventfd/actions/runs/1224765245