Remove and automate docs generation

[Blacksmoke16]

• Adds a GH Actions workflow/job that builds/pushes generated docs to a gh-pages branch
  • Runs on every push to master
  • Also builds docs for the required amq-protocol dependency
  • Makes navigating docs a bit easier as types are now correctly linked

Example build: https://github.com/Blacksmoke16/amqp-client.cr/runs/1126200835?check_suite_focus=true Example output: https://github.com/Blacksmoke16/amqp-client.cr/tree/gh-pages Example docs: https://blacksmoke16.github.io/amqp-client.cr/

NOTE: Currently Crystal docker images are a bit dated. Could update the image/remove the need to manually install rsync once there are more proper images resulting from https://github.com/crystal-lang/distribution-scripts/pull/68.

[dentarg]

@carlhoerberg WDYT?

[carlhoerberg]

I like that the docs are built for amq-protocol too. But can we get rid if the container and install crystal via snap instead? Less to download, less layers

[Blacksmoke16]

@carlhoerberg Probably, but would it be worth it? The workflow already only takes 30s with the container being 9s of that.

[carlhoerberg]

Thanks! updated the website to use the gh-pages branch