code: static Vector2d newUnitVector(final IAtom atom, final IBond bond) {
          return newUnitVector(atom.getPoint2d(), bond.getOther(atom).getPoint2d());
      }
docs: Create a unit vector for a bond with the start point being the specified atom.
  
  @param atom start of vector
  @param bond the bond used to create the vector
  @return unit vector