Add Typescript definitions

[electrovir]

This resolves #2

Simple solution which is mostly just a copy paste straight from the README. Comments included.

• I have read the contribution guidelines.
• I have added tests (we are enforcing 100% test coverage).
  • Not sure how to add tests for this.
• I have added documentation in the README.md, the docs directory (if
  any) and the examples directory (if any).
  • Also not sure exactly what to document, if anything, in the README about this.
• The status checks are successful (continuous integration). Those can be
  seen below.

[electrovir]

Should I update .all-contributorsrc?

[electrovir]

Example type tips rendered in VS Code:

[ehmicky]

Thanks a lot for this @electrovir!

Looks good to me overall. There are just few minor tweaks :)

You're right: no need for tests nor documentation.

[ehmicky]

@all-contributors could you please add @electrovir for adding this code?

[allcontributors]

@ehmicky

I've put up a pull request to add @electrovir! 🎉