Spent the evening getting the Python 3.9 build for PyOpenGL-accelerate running on Appveyor. In the end it was just knowing to add a tag "APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019" to the build-matrix for that one Python version so that it is built on the Python 3.9-compatible build-image. Will have to boot into Windows to test that it worked.

Also made a quick hack to do manylinux2014 builds (locally on my own hosts) using the docker images. Again, it's straightforward following the example project, but the missing bit is that you have to set PIP_PLATFORM=manylinux2014_x86_64 around (just) the call to pip wheel.

Also disabled Python 2.6 and 3.4 builds since they were failing on Appveyor (they were trying to build pygame from source to run the tests) and they shouldn't be too critically important any more.