Lack Of Type Definitions

[jameshopkins]

Typescript

Given that contrib/cursor already includes the relevant definitions, it'd be a shame not to copy those over into this project, and keep them up-to-date.

Flow

It would be advantageous to provide these to. See #10

[SimonMeskens]

I'd like this too, though I suspect the old typings have to be rewritten, now that Immutable is leveraging new features of Typescript