Remove m.prop + m.withAttr (#2317)

* Remove `m.prop` + `m.withAttr`

- For many uses, `m.withAttr` is *more* verbose than just directly using
  an event handler
- If you're using it with a bound callback, you're literally wasting a
  single character in the human readable version (and you're *saving*
  them in the minified output).
- It sometimes obscures your intent, if overused.
- Functions are easier to compress than `m.withAttr`, resulting in
  slightly smaller bundles.
- `m.withAttr` is overused anyways.
- `m.prop` is basically useless without `m.withAttr`, and the API
  doesn't have the same benefits it had with 0.2.x.

* Update changelog

examples/editor/index.html

@@ -28,7 +28,7 @@ var Editor = {
 	view: function() {
 		return [
 			m("textarea.input", {
-				oninput: m.withAttr("value", state.update),
+				oninput: function (e) { state.update(e.traget.value) },
 				value: state.text
 			}),
 			m(".preview", m.trust(marked(state.text))),