Migrate TCK userguide from jbake to asciidoc

[mswatosh]

The JBake plugin in use was old enough that it didn't support ARM based Macbooks. Updating the plugin caused other issues, so I decided to move from jbake to asciidoc, which is already in use in this repository for other documents, and is used extensively for other Jakarta Specification documents. This simplifies and speeds up the TCK build process, and should make maintenance of the userguide easier.

This PR covers:

• Migrating the Userguide form JBake to AsciiDoc
• Adds filtering for the index and release notes html files. This allows variable substitution, so the links in the tck docs work when built as either a SNAPSHOT or final release.
• Modernizes index.html to html5

Here's the docs folder of the tck since that's the easiest way to see the end result: docs.zip
Updated from Kyle's suggestions: docs.zip

[mswatosh]

@m0mus Would you be able to review this?

[KyleAure]

Thanks for taking this on. Just some minor comments.

[mswatosh]

I updated the JavadocAssertions to md, and merged the release notes and index.html into a single ReadMe.md. I also moved the pom.xml to the root of the folder and moved the ReadMe and JavadocAssertions so they're in the correct relative positions in the filesystem and final zip folder.