* Add GitHub Actions workflow for verification
Add a GitHub Actions workflow file that does the verification of pushes
and pull requests. I.e., it runs the linters, runs the tests, and builds
the website. This workflow runs for all `pull_requests` and `push`es.
* Add GitHub Actions workflow for deployment
Add a GitHub Actions workflow file that does the deployment upon pushes
to master. Before actually deploying, the linters and test are ran, just
in case.
* Remove Travis CI configuration file
* Remove unnecessary quotes from existing workflows
* Add caching for "Build website" verification
* Update build badge in README
Co-authored-by: Álvaro Mondéjar <mondejar1994@gmail.com>
