Build with cibuildwheel

[mattip]

Add real work to the github CI using cibuildwheel

[mattip]

When I tried this on my fork, it failed, but I think it should be merged anyway as the first step towards building wheels easily. The status:

• passes on linux
• there is a failing test on macOS with CPython 3.10 in vmprof/test/test_run.py
• there is a failure to build on windows with CPython 3.10: ssize_t is missing
• PyPy 3.7 on linux fails to build the c-extensions used in tests, I think those tests should be skipped for PyPy.

Additional work is needed to

• get 3.10 working on macOS and windows
• add wheel uploading to CI
• ~remove appveyor and most of the travis CI runs.~ (travis is only running arm64 and failing)

[mattip]

Closes #241 related to #240, #230

[mattip]

I think I have taken this as far as it can go right now. Fixing the failing tests and adding the deploy incantations can be done on subsequent PRs

[mattip]

Rebased after #239