chore(rebuild): CI: Switch to using GitHub Actions (#21)This change s…

…witches the CI setup for the repo away from Travis and overto GitHub Actions, using https://github.com/w3c/spec-prodIt also renames the spec source file to index.bs, to follow Bikeshednaming conventions, and it removes the generated output file(index.html) from version control in the repo.

SHA: 42022be
Reason: push, by @sideshowbarker

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>