#8 complete operator compatability by adding inplace operators, and make them all polymorphic for number and tuple types

[Nathan Oostendorp]

Right now we support the following operators: +, -, /, *, &, |, -(unary negative)

+, -, & and | all support the parameter as either an Image object or a number -- and route appropriately to the OpenCV function ie Add or AddS ("add scalar")

I would like to support the +=, -=, &= etc operators which modify the elements in place, rather than creating a new bitmap. And I would like all functions to optionally accept a color tuple (R,G,B) so that channels could be addressed individually. So for instance:

i = c.getImage()
i -= (0, 255, 255)  #blacks out the green and blue channels