GIF Player: add on change props to listen to gif play/pause

[AquiGorka]

@benwiley4000 hello again, another PR here:

This changes introduce an onChange prop to listen to changes in the gif state (play/pause).

[benwiley4000]

Also I'm thinking about it and we could probably me more descriptive than "onChange". Maybe "onTogglePlay" or something? In case we have to add other handlers later on.

[AquiGorka]

I prefer the form:

if (typeof this.props.onChange === 'function') {
this.props.onChange(...);
}

Added destructuring with default value, let me know if this is alright with you.

I also prefer handling this in componentDidUpdate - we can just check if the playing state is different than the last.

Done.

Semicolon would be great. 😉

;)

[AquiGorka]

@benwiley4000 will you let me know when you update on npm? I have an app eager to use this update ;)

[benwiley4000]

@AquiGorka yep it's out! v0.4.0. 🙂