Explore github actions

[albop]

Goal would be to automate

• tests (currently linux only)
• release on pip and conda synchronized with git tags.

[albop]

We use github actions for:

• test: pytest suite for every push (in any branch)
• pypi release: when a version is tagged in master branch. This should trigger an automatic pull request to update the conda recipe, which must then be merged manually.
• documentation: on every commit in the master branch