Vector2D.h
Vector2D.cc           :  a 2D vector with sum and multiplication by a number
Vector3D.h
Vector3D.cc           :  a 3D vector as a 2D vector plus a z coordinate
testVector3D.cc       :  create and print a 3D vector
testVector3DPrint.cc  :  add a function to print the modulus, taking 
                         a Vector2D argument by 
testVector3DPrRef.cc  :  add a function to print the modulus, taking 
                         a Vector2D argument by reference

to compile:
c++ -Wall -o testVector3D      testVector3D.cc      Vector2D.cc Vector3D.cc
c++ -Wall -o testVector3DPrint testVector3DPrint.cc Vector2D.cc Vector3D.cc
c++ -Wall -o testVector3DPrRef testVector3DPrRef.cc Vector2D.cc Vector3D.cc
