Zoom which is idempotent to the order of application

[mateja176]

First of all, thank you very much for all the work you've put into panzoom, you've created a truly awesome library!

On the other hand, according to the type declarations, both zoomTo and zoomAbs accept a clientX and a clientY.

The issue is however that the order of applying zoom operations matters. For example, you are not going to end up in the same state if you first apply action A (zoomAbs(100, 100, 1.1)) followed by action B (zoomAbs(200, 200, 1.2)) compared to applying action B followed by action A.

It'd be handy to have an operation which is idempotent to the order of application, similar to moveTo, but for scaling. For example, it may accept x and y coordinates as well as a scale value.