Minor bugfix release, moving Continuous Integration from Travis/AppVeyor to
GitHub Actions, based on changes on master, but without the (more invasive)
(test) fixes for Windows.

• Fixes

  • Fix hideframe decorator for Python 3.8+ (#263)
  • Fix hidden_frames discrepancy with IPython (#426)

• Misc

  • ci: move to GitHub Actions (#444, #445)
  • ci: use .coveragerc (#304)
  • qa/flake8 fixes
  • test fix for newer PyPy3