Simplify events handling

Let's replace current events system with three kind of events (similar to set handling)

• add - when new value is added (separate event per each added value)
• delete - when value is deleted (separate event per each value pair)
• change - whenever some change occurred in array
  • It can be called once per many simultaneous changes,
  • It also can be called when in summary no changes to what values are contained has been made, but order of values in array have changed.
  • It should also be allowed (for performance reasons) to emit change when change not necessarily may have occurred (and compute of whether it indeed occurred is expensive).
  • This event doesn't suppress add and delete, it's supplementary to first two.

Array is technically a map (index/value pairs), so it may feel more appropriate to use map-like events system (set & delete). However this can be expensive and not that needed. Imagine we shift element from large array. All index/value mappings in array have changed, so in such case we would have to emit set events for each value. While for most cases two events delete and change will provide all we need.