Update src/utils/math/class.vector2D.js

Added a bunch of useful functions.  I changes the standard math functions to return a new vector instead of changing the value and added special functions that will modify the value if the user wants to. they end with "Equals".
EXAMPLE:
vec1.addEquals(vec2);

vec3 = vec1.add(vec2);

this will require some changes in other code aswell.  I will try to find them and make those changes tonight.