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

docs/simple-application.md

@@ -471,12 +471,12 @@ module.exports = {
 			}, [
 			m("label.label", "First name"),
 			m("input.input[type=text][placeholder=First name]", {
-				oninput: m.withAttr("value", function(value) {User.current.firstName = value}),
+				oninput: function (e) {User.current.firstName = e.target.value},
 				value: User.current.firstName
 			}),
 			m("label.label", "Last name"),
 			m("input.input[placeholder=Last name]", {
-				oninput: m.withAttr("value", function(value) {User.current.lastName = value}),
+				oninput: function (e) {User.current.lastName = e.target.value},
 				value: User.current.lastName
 			}),
 			m("button.button[type=submit]", "Save"),