Generate *.d.ts and sourcemaps

[mlhaufe]

Generate *.d.ts and sourcemaps to resolve the following issue for consumers:

I have a suspicion this would require #28 to be implemented. Hopefully not.

[mlhaufe]

Refs:

• https://codewithhugo.com/jsdoc-typescript-typings-types-d-ts/
• https://voxpelli.com/2019/10/use-type-script-3-7-to-generate/
• https://www.typescriptlang.org/docs/handbook/declaration-files/dts-from-js.html