fix: improve types

[mihkeleidast]

Resolves #109.

This will allow importing of the additional types. For testing, this is now valid TS:

import whatInput, { InputMethod, Strategy } from 'what-input';

const handleInputChange = (type: InputMethod) => {
  console.log(type);
};
whatInput.registerOnChange(handleInputChange, 'intent');
whatInput.unRegisterOnChange(handleInputChange);

const getInputMethod = (strategy: Strategy) => {
  return whatInput.ask(strategy);
};

[ten1seven]

Thanks @mihkeleidast and @greypants! This has been published to NPM as version 5.2.10