Pinch to zoom on touch screen devices

[verhovsky]

and tap+drag don't work.

[floooh]

Deleted my previous comment since I didn't notice that this is in the v6502r repo, and not in the sokol repo. Yes, pinch-to-zoom would be useful, but so far gesture recognition isn't supported by the underlying sokol libraries. I'll keep the issue open since eventually it would make sense to implement it, but on the other hand, the v6502r projects isn't mobile focused.