Tooling updates

[luin]

Major changes:

1. Migrate docs from Jekyll to Gatsby in order to ditch Ruby dependencies.
   • Template engine changed from Jekyll's Liquid to MDX 2.
2. Migrate tests from Travis CI to GitHub Actions.
3. Update all dependencies.

Regressions:

1. Support for redirect_from is removed for simplicity.
2. examples in the release folder is removed for simplicity.