implement class Vector2D, Particle and ParticleSystem
add generic, with lots of bugs
fix typo in README
change use of collections
merge branch 'master' into generic: fix README
fix problems with standard library using, remove generics
store dirty design
start re-design
fix package yphysics
Merge branch 'generic'

Conflicts:
	assignment-03/NBody.java
	assignment-03/yphysics/Particle.java
	assignment-03/yphysics/ParticleSystem.java
	assignment-03/yphysics/Vector.java
	assignment-03/yphysics/Vector2D.java
add toDouble for Vector
fix makefile
fix assignment-03, finally
make all things right for this
add full comments
finish assignment-03