[Suggestion] provide similar hook API to Formik and use-form

### Are you submitting a **bug report** or a **feature request**?

Currently the only way to use react-final-form is inside a render component - this makes it painfully non-react to do certain things like passing control of the submit or form state outside (to the parent) of the render component.

Can react-final-form provide a `useForm()` hook similar to how Formik and use-form pkg's offer the ability to simply create a "form state" from the hook call without a wrapping component or context provider?

I love react-final-form and use it in all my react and react-native projects but it's lacking in this specific area.