Make onChange handler optional

[deepakjois]

If I do no specify an onChange handler, for e.g.

 <RadioGroup ref="deliverymethod" name="deliverymethod">
...
</RadioGroup>

I get an error:

Uncaught TypeError: Cannot read property 'bind' of undefined

Does the onChangeHandler need to be set. Can’t the React element maintain its own state, and update it when the value changes.

[chenglou]

If you don't provide onChange, you'll receive the warning that the handler's not set, because the library allows only controlled components for now. Maybe we should implement uncontrolled components, but that gets slightly messy.

[briandamaged]

I just created a PR that allows both the "onChange" and "selectedValue" properties to be optional. If neither property is specified, then React will treat the radio buttons as uncontrolled components.

[nkbt]

Fixed by #22