Missing type definitions

[jfstephe]

Hi,
Thanks for the library. Any plans to add typescript type definitions?
John

[jasonray]

@jfstephe I've not done that before, but happy to. Could you give me a hint on how-to? If not, will look up later this week.

[jasonray]

@jfstephe : Could you review to determine if this looks appropriate #116