1.1.0: Use rouge for source highlighting

This version enables rouge as a default source code highlighter for all documents.
The source highlighter can be overwritten in a document header with the :source-highlighter: <value> attribute.

1.0.1: Fix Ruby base dependency

Asciidoctor-pdf doesn't support Ruby 3.x yet, and the ruby:alpine image
recently moved from 2.x to 3.x. The parent image is now explicitly declared as
ruby:2-alpine, which is pinned to 2.x. This should fix builds across the board.

1.0.0!

This action enables asciidoctor builds including mermaid diagram support. It supports regular or pdf asciidoctor invocation, sets up the whole mermaid environment, and can pass arbitrary arguments to the asciidoctor executable. It also takes a set of files, which can contain regular globs or double-star globs.

Lastly, the action outputs asciidoctor-artifacts, the name of the directory that the built files were placed in, for use by follow-on actions.