vector of size 3, for Cartesian coordinates

Constructor:

Vec3(x,y,z) - initialize with x,y,z values

Use:

  A Vec3 emulates a sequence object, so elements can be set and queried in the 
  usual fashion.
  Vec3s can be added, subtracted, scaled using the normal operators (+-*/).

Additional functions:

norm(vec)        - return sqrt(x^2+y^2+z^2).
dot(vec1, vec2)   - return the dot product of two vectors.
cross(vec1, vec2) - return the cross product of two vectors.
unitVec(vec)      - return a unit vector in the direction of vec.