Document how to use easings

[Jörn Zaefferer]

The documentation needs to answer this question: How do you use easings with jQuery UI effects?

Currently we have the easing showcase demo, hidden under effect: ​http://jqueryui.com/demos/effect/#easing

The API documentation for the effect-method mentions that is accepts options, but doesn't provide any details at all, also excluding how to specify easings using that option.

I suggest creating a simple demo under a new "Easings" header, with a single element animated with the easeOutBounce easing; then put the canvas-showcase as an extra demo under that header.

Also update the effect-API docs to describe the properties the options-argument expects.