Add support for providing value to onChange

[andyrichardson]

If the argument to onChange is not an event, use the value as a value setter.

This will help native users #35

Work may be required to differentiate between an event which replaces state and toggles state.

Toggle (currently the case when event target is a checkbox)

// ['checkbox1']
onChange('checkbox2')
// ['checkbox1', 'checkbox2'] 
onChange('checkbox1')
// ['checkbox2'] 

Replace/set state

// ""
onChange("John")
// "John"
onChange("Carla")
// "Carla"