Request / small ideas

[kergekacsa]

Hi Andreas,

First of all, thanks for maintaining PhotoSwipe, good work! :)

I'm currently using it a private project for which I need to modify it (to let next and prev buttons grow to fill the empty space next to the image) and I got one performance idea and a small idea/request to make it more easier to use it :)
1.) It would be wise to use some kind of throttling on window resize, on a simple resize it got called a lot of times.
2.) There could be an afterZoom _shout event fired after (what a surprise ;) ) zooming in/out.