Allow implicit cycles

[devagrawal09]

After implementing #1, allow emitting events inside event handlers.
Emitting events inside the pure part should add on to a stack. Listener queue should be a 3d queue, where the first dimension is mutation listener vs user listener, second dimension is the position in the stack (how deep into nested emissions we are).
Once all the pure transformation, including all nested emissions, are complete, run listeners in 3d order depth first.