SAM-209 organize documentation

[eapearson]

This set of changes is designed to satisfy SAM-209. It attempts to do so by:

• moving documentation into a single /docs directory
• organizing documentation within that directory
• providing an index page which links to each document
• moving detailed documentation from the canonical README.md into separate documents
• refactor README.md according to https://github.com/RichardLitt/standard-readme
  • adding standard sections
  • fleshing out content in this sections
  • refers to documentation for further details
• adds an example of PlantUML diagramming

In addition, I've cherrypicked a few new documents from SAM-96, from which this work was initially copied. This is because this set of changes should also satisfy the needs of the changes for SAM-96, which needs to add several documents and diagrams. Separate from SAM-209, it was requested to remove the document reorganization from SAM-96, so adding these additional changes here allows us to base those changes on this work.

[eapearson]

I see the release notes in the docs directory. I think I would prefer to keep those at the top. I see it is empty so maybe the intent was something else.

That was intended to be a document about creating release notes, as it is located in the documentation directory of the docs directory. I've updated the empty document to have a title and a quote-blocked reminder to complete the content.

There is already a RELEASE_NOTES.md in the project root.

Interestingly, I've found that some Python projects locate release notes within the documentation folder, not at the project root. I found this a bit baffling at first, but it does make some sense, as it could be argued that for a documentation set to be complete it should include a description of the evolution of the product over time, including release notes.

[eapearson]

Resolved a new merge conflict introduced by concurrent changes to RELEASE_NOTES.md