Add directional light; move boop to boulder.
So following proper OOP doctrine I put the "boop" noise audio player node
into the Boulder scene because boulders boop when they are created so
that's obviously the responsibility of the boulder class, eh? Yet, this
seems less efficient than having one reference to the player in the
toplevel context and playing the noise "externally" as it were (the way
it was before this change.)
Whatever. On the gripping hand, no machine likely to play this program
will struggle with this, so it's fine.