Scaling limits and panning boundaries prototype

[dalyr95]

Brilliant library, math is not my strong point, but I was able to get my head round what the interactive functions were doing.

In two days I had to implement a pinch and zoom library with scaling and panning boundaries and I've pushed the code to this repo; https://github.com/dalyr95/zoom

Feel free to implement anything that catches your eye and if you have any questions let me know. It needs to be cleaned up massively and the math done by someone whose actually good at it.

Demo here; https://github.com/dalyr95/zoom

[paolobenve]

I'm going to prepare a pull request, if @anitasv agrees to include the change