switch CI off travis-ci

[willkg]

Bleach currently uses Travis CI for thing, but it seems like Travis CI is going to go away. We should switch to something else.

A lot of Mozilla projects use Circle CI, so I think that's probably the best option for now.

[g-k]

see also: #331

[willkg]

I was just reading through this post which talks about setting up github actions and testing across linux, macos, and windows:

https://dan.yeaw.me/posts/github-actions-automate-your-python-development-workflow/

Figured maybe that would be helpful.

[g-k]

Awesome, that looks great! Thanks willkg

Also, I'm +1 on publishing to pypi from CI (so we don't have to manage pypi creds on our laptops).

[hugovk]

Please see PR #514 for testing and linting on GHA.

You'd need to keep Travis at least for Python 3.7 and 3.8 until #503 is fixed, but some jobs could be removed from Travis.

Some things that Travis has but GHA doesn't, which could be useful: 3.8-dev and 3.9-dev. Also up to 4 different CPU architectures (eg. one is big-endian), but that's probably more useful for projects with C code.