v3 docs

[ethanresnick]

Among other things, Document Adapter contract, including that Adapter.find must remove duplicate resources.

Ideally, I'd like to have: 1) a website with manually written docs that are much more thorough; and/or 2) some auto-generated docs based on my type signatures + jsdoc comments, which could provide the basis for a docs site.

The trick around auto-generated API docs is that there doesn't seem to be a perfect tool for it yet:

• API Extractor mixed with API Documenter seems like it could be perfect, but API Extractor still uses an old version of TS, which doesn't support some of the TS features we're using. See [api-extractor] Update Typescript dependency? microsoft/rushstack#689 Also, the errors API Extractor gives are quite cryptic. That said, it's very robust in making sure I've clarified what's intended to be public and what's private, and exported all the public types.

• Type Doc is also on an old version of Typescript, but seems like updates there have been blocked even longer, and its API auditing is far less thorough/useful.

• Finally, there's Tygen, which is nice in that it does support newer Typescript versions, but seems pretty immature/beta. It threw an error when trying to run it over json-api.