trivial: Post release version bump
Use 256ms as the smallest sample duration

64ms was too small to be used on CRT displays, so use a duration that will
encompass at least 10 refresh cycles on a display with a 50Hz refresh rate.
Speed up the auto-scaled measurements considerably

By taking all three channels simultanously we can speed up the sample process,
at the slight expense of the precision of dark channels when another channel is
saturated.