Convert to TS or supply ambient definitions

[chriskrycho]

As part of Ember.js RFC #0800, this package needs to supply type definitions. Preferably, this would happen by converting to TS and generating from the source; as an alternative, it can publish ambient types (presumably starting with the ones on DefinitelyTyped).

All the members of the Typed Ember team are happy to advise on how to do this; feel free to reach out in #dev-typescript on Discord if you have questions!