Start of force calculations
Merge branch 'master' of https://github.com/johanjoensson/TFYA50-Computational-Physics
Force calculation done, not tested
Merge branch 'master' of https://github.com/johanjoensson/TFYA50-Computational-Physics

Conflicts:
	Code/Project_v0.01/Project_v0.01/world.cpp
	Code/Project_v0.01/Project_v0.01/world.h