Sprites should have a nicer toString method?

[hallpell]

Currently converting sprites into strings just gives "[object Object]" which is not useful (and therefore is basically a mistake every time it happens). I'm considering making it slightly more informative, probably something like "[TYPE@(x,y)]".

The main reason I think this would be useful is when teaching cloning, you could then display the array storing the clones as text and see them moving about to demonstrate that we're keeping track of all of these.