Only document the exported API, not every symbol

There is more work to be done, because this filters out more
than desired, and we don't have events documented yet.
Nicer way to fix @inheritDoc
Adding params of API symbols to the API

This makes the API docs complete. What still needs to be
documented is API events, but this deserves a separate pull
request.
A few lines explaining what the exports.js plugin does
Adding the projection namespace
Making the linter happy

Although *.jsdoc files are none of the linter's business...
Use a public return type for a public function
Making @elemoine and GitHub happy

Reminder to self: everyone wants a new line at the end of a
file.
Don't use the undocumented property before it is set

This actually avoids addition of params of symbols that are not
part of the API.
Remove "Inherited from" for non-API parents
Merge pull request #527 from ahocevar/jsdoc-filtered

Only document the exported API, not every symbol. r=@elemoint