Added animation merging (#27)
Passed animatedBones in a new stop(...) method within playOnce() to only stop bones that are also in the new playOnce animation
Set new resume boolean to true in tick() method to start the animation from the tick the other bones are at.
Created second stop method which only stops the bones that are passed in the params. Used to keep the rest of the bones playing on the background while a playOnce animation overrides the bones in the set.
Added resume boolean to play method, if set to true the code will find the first bone that isPlaying and take their tick as starting tick
Added resume method which is the same as play but with a specific tick
