Typescript support

[virzak]

Feature request

Add typescript to this library and redux-promise-listener

What is the current behavior?

There is no typescript support

Other information

We have a large project that uses redux-saga with redux-form. Typescript is used for everything and it all works smoothly. DefinitelyTyped definitions for redux-form are quite mature. Lack of definitions for this project and lack of tests for react-final-form make it difficult to migrate to the point where it might not be worth it.