[WIP] test: add dtslint, and add typings test file

[ChristianMurphy]

⚠️ work in progress ⚠️

This

• adds dtslint, a tool to test typescript definitions.
• documents minimum typescript version needed to use typings
• adds a typings tests file based off the simple example.
• adds doc comments based off API docs
• tests typings on Travis CI
• updates Travis CI to test on Node 10 and 12 LTS versions

TODO

• fix typings to support simple example
• resolve dtslint errors

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[stramel]

Check #1535 for updated types.

I think adding the testing around it would be great once we get that merged which will put us significantly closer to the actual API definition.

As for docs in the file, I don't see a benefit to maintaining/synchronizing the docs between the API.md file and the index.d.ts. I was actually looking for a way to generate the API docs automatically based on JSDocs using index.d.ts file. I think that would be preferred.

[ChristianMurphy]

I think adding the testing around it would be great

Agreed

once we get that merged which will put us significantly closer to the actual API definition.

I trust that progress is being made, having tests can be a nice approach to measuring progress and ensuring no regressions crop up.

As for docs in the file, I don't see a benefit to maintaining/synchronizing the docs between the API.md file and the index.d.ts. I was actually looking for a way to generate the API docs automatically based on JSDocs using index.d.ts file. I think that would be preferred.

That's the same idea I'm working toward.
Moving the docs into the typescript definition.
Then having one of:

• https://github.com/microsoft/tsdoc
• https://typedoc.org
• https://api-extractor.com/pages/setup/generating_docs

convert it into markdown, html, or any other format desired.