Add method sprite:has_animation(animation_name)
Created by: Renkineko
In the case of the builtin entity coded in lua, it could be useful to check if the sprite has the animation wanted (example : you want your arrow do an automatic animation when the move stops, but some other just want it to be removed (imagine an ice spell acting like an arrow so using the arrow entity, it is possible to just make it disappear), so we need to check if the "arrow_stop" animation exists, if yes play it else do other stuff...