Observe attributes for #637

[justinbmeyer]

Pertaining to #637, this pull request lets you listen to when HTML attributes change. For example:

var div = $("<div>")

div.bind("attributes", function(ev){
  ev.attributeName //-> "foo"
  ev.oldValue //-> null
  ev.type //-> "attributes"
})

div.attr("foo","bar")

It integrates directly with jQuery and Zepto's attr,and removeAttr, Mootool's set, and Dojo's dojo.setAttr and dojo.removeAttr.

It's tested against live-binding so that changes to attrValue in the following will fire attributes events:

<div foo="{{attrValue}"/>

Attributes with jQuery works via MutationObserver in browsers that support it. No other library uses MutationObservers. All browsers should work, but I have not tested IE.

[justinbmeyer]

merged this into minor myself ...