add 'update' events for zoom and drag.

[endel]

This pull request allows listening to zoom and drag changes, triggered by mousemove event.

[sandstrom]

@endel Thanks for participating!

Can you describe a bit more about what this change does:

• Does it fix a bug or add new functionality?
• When is this feature useful?

[endel]

Hi @sandstrom!

Does it fix a bug or add new functionality?

It adds new functionality.

When is this feature useful?

By listening to pz_zoomupdate or pz_dragupdate, you can interact with external elements given the current state of the PinchZoom. e.g. animate a progress bar given the current zoom factor, or move something else on the screen at the same time the drag is happening.

Hope this helps,
Cheers!

[sandstrom]

Got it, thanks!

Merged now. I appreciate your participation! 🏅