Add a TypeScript definition

[mahnunchik]

It wold be nice to add a TypeScript definition.

Related: electron/forge#1755

[malept]

See electron-userland/electron-installer-snap#72 for an example of how to do it.

[ffflorian]

I created a PR on DefinitelyTyped: DefinitelyTyped/DefinitelyTyped#54338

[malept]

I would actually prefer an in-package definition type rather than a separate one.

[ffflorian]

What do you think about rewriting this in TypeScript? It's not that much work.

[ffflorian]

I opened a PR for the definitions @malept :)

[malept]

What do you think about rewriting this in TypeScript? It's not that much work.

I would be hesitant to convert this to TypeScript mostly because I need to see how comprehensive the testsuite is first.