[DO-NOT-MERGE] Toolset for combining coradoc & reverse_adoc

[hmdne]

This PR is NOT intended to be merged. It is merely a showcase of our current work at merging reverse_adoc into coradoc. A request for comments of sorts.

We will proceed with this merger once all remaining pull requests in reverse_adoc repository have been merged.

The approach is to use a migration script to:

1. Modify reverse_adoc, to create a repository in a state of no files having a duplicate name with coradoc repo
2. Rename ReverseAdoc class to Coradoc::ReverseAdoc
3. Git merge reverse_adoc into coradoc
4. Merge other contents manually
5. Finally, change reverse_adoc repository into a stub repo, so that users of reverse_adoc will have a clean path to update.

This approach will preserve git history for both repositories, merging them together.

Ref: #51

Metanorma PR checklist

• [ ] Breaking changes (list related PRs)
• [ ] Documentation update required (create task for this)
• [ ] External dependency introduced (documentation update need)
• [ ] Gem with native library introduced

[hmdne]

Merge has been completed. Closing this commit.