Returns the angle between line segments.
If the line segments intersect, the acute angle between the lines is returned. If the lines join at end points, the smaller of the two angles is returned. If there is an error, a negative value is returned. The result is an angle in the range between 0 and pi, or between 0 and 180 if the third parameter is true.
Parameter 1 - a two point line segment.
Parameter 2 - another two point line segment.
Parameter 3 (optional) - A Boolean flag indicating that the function should return an angle in degrees. If omitted, the default unit is radians.
Returns: a real value in the range between 0 and pi (or between 0 and 180).