XSpec support under XProc 3.0

[wendellpiez]

Committer Notes

XSpec runtimes using XProc 3.0 pipelines.

• [x] XSLT
• [ ] XQuery
• [ ] Schematron

Along with:

• [x] Installation pipeline
• [x] Smoketest pipeline
• [x] Batch processing pipeline (simple, with one for one results)
  • [x] producing HTML
  • [x] producing JUnit XML

All Submissions:

• [ ] Follow Contributing guidelines
• [ ] Make no changes duplicating or conflicting with other open Pull Requests
• [ ] Have been squashed to keep only relevant interim commits, if any [instructions]
• [ ] Have been tested manually
• [ ] Pass all CI/CD checks

Changes to Core Features:

• [ ] The Issue history, discussions and new documentation provide context for new features -- everything is reasonably self-explanatory
• [ ] New tests are included
• [ ] New examples are included
• [ ] Everything in readme and TESTING documents has been updated

[wendellpiez]

If possible I should probably try adding XSpec for Schematron and XQuery before merging this.

However, getting extra eyes on what it does so far would be groovy. 📻

One question: where are there still gaps in documentation (as this grows a little more complex).