freezeframe should have a "ready" event listener

[eballeste]

Because the internal setup method is promise-based acting upon the freezeframe elements after initializing it might sometimes render incorrect results. It would be cool if we could have some type of ready event listener that is triggered after the private _ready method is called.

[paulm17]

Just want to add my +1 to this also.

I tried to clone and fork the project but kept on getting npm issues. Honestly, I've moved onto yarn now.