PixelFormat {red,green,blue}_max should be 2**n - 1
PixelFormat {red,green,blue}_max should be 2**n - 1

Rather than store the 2**n - 1 value, we store the n, so that
we can quickly shift right a pixel to encode it for transport.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

djs55/ocaml-vnc