feat: add type definition

[adenvt]

Add type definition for typescript user

[romainmenke]

Hi @adenvt,

Thank you for your contribution 🎉

Personally I don't find it is maintainable to have a manual .d.ts file.
I think that this places the highest burden on maintainers and provides the least value/assurances.

So I don't think we can accept this even if I appreciate your effort.

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However I would consider a change that adds JSDoc type annotations.

Benefits of JSDOc annotations:

• can be tested
• helps maintainers to write better code
• .d.ts files can be generated from them

Stylelint for example uses such a setup : https://github.com/stylelint/stylelint

[adenvt]

@romainmenke Thank for reviewing.

I'm update it, and follow your approach to use JSDoc and generate .d.ts from it. I did:

• Add script npm run build-types to generate .d.ts
• Update lib/index.js to has more strict type.
• Update script/clean.js to remove types/* before build
• Update .gitignore

[romainmenke]

@adenvt Thank you for your contribution!

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I've made a few more edits:

• ensure that types are present in git, as this makes them visible on GitHub
• add types to sources.js
• add type checks with tsc
• fix some internal issues surfaced by the type checks.