ANGLE (x, y)

   Synopsis:
      Returns the angle, in an anti-clockwise direction, between the positive
         x-axis and a line from the origin to the point (x,y)

   Notes:
      The return value is always in the range -180 > @ >= 180, assuming that
         OPTION ANGLE DEGREES has been specified. Otherwise, the return value is
         the equivalent angle measured in radians.
      x and y must not both be 0.
