Post Events

* Added post events to renderEntity and renderCollection
* Each event includes a 'payload' param that's an ArrayObject (to keep
  state). They also include entity/collection params, respectively, if in
  case the original entity/collection is needed.
Does this work on ArrayObject?

(/me goes off to test...)

Color me suprised! I figured you'd need to cast using `getArrayCopy()`. Nice, discrete optimization here.