Complete chapter 9 project.

9_high_level_language/(Particle, Simulation).jack
	-Complete my chapter 9 project.
	-Complete `Simulation.run()`; add logic to handle particles that
	move past the borders of the screen.
	-Define `Particle` methods `getX()`, `getY()`, `setX()`,
	`setY()`. `setDx()`, and `setDy()`.