Add api Docstrings from some source (e.g., MDN)

[simonegiacomelli]

Primary goal: provide minimal docstrings on the Apis.
Secondary goals:

• open up and pave the road to adding compatibility informations aka supported platforms (see issue
• add a link to mdn docs when available

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The MDN content markup may be a good source of structured data to harvest (and its html counterpart).

Also notice some comments in a json file from TypeScript-DOM-lib-generator; probably used to fuel Typescript stubs comments (don't know how this json is made).

Another source to investigate probably generated from Typescript stubs.

[simonegiacomelli]

Interesting article about the MDN transition from html to markdown

[simonegiacomelli]

Yari is the code that renders MDN Web Docs.
This folder contains the KumaScript macros used as part of the rendering; they are interesting because they are used to process inter-page links.

[simonegiacomelli]

It looks to me that the best course of action is to use yari and the MDN markdown.

One interesting read is about compatibility tables and BCD (Browser Compatibility Data).