Migrate to Github Actions

[maximlt]

Supersede #66

[maximlt]

@jbednar the CI has now been migrated to Github actions and is all green. I had to remove Windows-py2.7 from the test matrix, it raised an error while installing ipykernel in thedoit develop_install step for which I found no easy fix online. Note that the test suite on py2.7 is only running test_unit, it ignores test_examples and test_unit_extra. The docs and releases are built based on tags, similarly to the other holoviz projects.

The failing AppVeyor tests that are shown in this PR can be ignored I think, I've deleted the appveyor configuration file.

You might want to check that the expected secrets (CONDA_UPLOAD_TOKEN, PPU, PPP, ACCESS_TOKEN, GITHUB_TOKEN) are well configured in the repo's settings, to which I don't have access. You might want first to tag a dev release to check that the docs and release workflows work well, before trying to do a proper release.

[philippjfr]

You might want to check that the expected secrets (CONDA_UPLOAD_TOKEN, PPU, PPP, ACCESS_TOKEN, GITHUB_TOKEN) are well configured in the repo's settings, to which I don't have access. You might want first to tag a dev release to check that the docs and release workflows work well, before trying to do a proper release.

They are configured for the whole holoviz org, so they should be available.

[maximlt]

Ok sweet good to know!

[jbednar]

Fabulous; thanks @maximlt ! I'll merge and we'll see how it goes!