Suggestion: fire the recalc_and_tick function upon window.load also

[dustMason]

I faced an issue where sticky-kit could not properly determine the height of the parent element because it contained a bunch of images without fixed heights. Although other solutions exist with subtly better features, simply firing recalc_and_tick as a $(window).load() callback is good enough for my current needs.

I think this might be a common problem for others. I would create a PR but since this is such a simple one-liner and I'm not using the code in this repo directly I will just create this issue.