Improvement: Typescript Support

[LukasOchmann]

Wouldnt it be nice to implement Typescript, as it improves Readability, Mantainability and it improves the Developer experience?

[MickL]

For the developer experience there is @types/node-persist at least. Anyhow I would like to see the types be part of this project instead of within @types. This would be way more convenient for the developers and the maintainers can more easily maintain the types.