Starts this TweenChain playing.
You only need to call this method if you have configured this TweenChain to be paused on creation.
If the TweenChain is already playing, calling this method again will have no effect. If you wish to
restart the chain, use TweenChain.restart instead.
Calling this method after the TweenChain has completed will start the chain playing again from the beginning.
This TweenChain instance.