Add initial automatic play testing feature
* 'make test' runs automatic play test. It plays the game
from start to finish automatically, without any user
intervention and as fast as possible (without delays)
and checks that everything looks as it should be.
This play testing uses the textual ASCII "renderer", so this
visual representation is tested at the same time and no
graphical or TUI libraries are needed. Of course any 2D or 3D
representation is not tested by this test, but as
the different visual representations should be very
simple (only show the current situation visually, possibly
doing linear interpolation for the motion of crates), and all
the logic and animating is done in inside the game, the game logic,
animating and playability should be pretty comprehensively tested.