Basic Operators implemented for LineScan

Add, Subtract, Multiply, Divide operators implemented for LineScan objects.

Example:

    img = Image('lenna')
    l1 = img.getLineScan(x=20)
    l2 = img.getLineScan(x=200)

    l3 = l1 + l2 #to add LineScans
    l4 = l1 - l2 #to subtract LineScans
    l5 = l1 * l2 #to multiply LineScans
    l6 = l1 / l2 #to divide LineScans