Add a flag to document all exported bindings

[arv]

This adds a boolean flag called document-exported (defaults to false)
that effectively adds an empty comment to all exported bindings that do
not already have a JSDoc comment. It also does the same for the
members of exported classes and objects.

export class C {
  method() {}
}

Both C and C#method are now part of the generated documentation.

Related to #424

[tmcw]

👍 awesome, there's a lint error - I think here - that's making CircleCI quit

[arv]

That was not the lint error... See new commit if you care.

[arv]

Test is timing out. Maybe I've made test/bin.js too slow by adding one more test to it?

2 observations working on this:

1. It might be better to move the code into an infer pass. However, infer passes only update existing comments. Can it work to add new comments in an infer pass?
2. If there was a way to add options to a fixture test testing this would have been cleaner.

[arv]

If you like #492 then I can simplify these tests to use that.

[tmcw]

Yep, can you rebase on master and check that tests should pass? Still timing out, digging more.

[arv]

@tmcw PTAL

[tmcw]

@arv looks great! In terms of:

It might be better to move the code into an infer pass. However, infer passes only update existing comments. Can it work to add new comments in an infer pass?

+1 for creating an interface for extracting comments just like we have one for inference. I don't think the inference interface (ha?) makes sense for extraction, so I wrote #502 which creates an 'extractor' concept and then extracts the two kinds into their own files. It seems to work pretty well - the only weirdness is around addComments, which I inject into the extractors so we don't have to pass arguments everywhere. Thoughts? If you're into it, you can cherry-pick the commit over.

[tmcw]

Merged with #502!