Add documentation for types and their members

[srujzs]

We should likely fetch data from the MDN and auto-annotate IDL types.

[parlough]

Another thing I'd really like to see is surfacing browser support or baseline information on the API docs. This past week they adjusted the baseline definition to have "Newly available" and "Widely available" as well. They have an npm package to access this data.

Eventually this could even be used to add something like support metadata/annotations to the generated members. Then we could have a lint (or similar) that triggers on any unguarded usage of an API that's not in the "Widely available" category, or at least "Newly available".

[devoncarew]

The data from the web-features npm package looks like a better source of feature info than the web-specs one I started pulling from (#111).

[devoncarew]

This is mostly done; we can track remaining work / improvements in more specific issues (eg. #190).