Add support for an inView callbaack

I have a need to be able to set a state var once the chart is in view and the animation has started. Unfortunately I cannot rely solely on the events from the chart, I am using `onComplete`, but in adding this plugin, `onComplete` is immediately fired on startup, even if the chart isn't in view, which causes problems for me. I have yet to determine why `onComplete` is firing. Long story short, it would be helpful to have a callback/event like `inView` that fires once the chart scrolls into view. This would allow me to ignore the `onComplete` events until after this callback event happens.