Added several options.
-I num: override the interlacing value read from the YUV stream.
-s num: Allow the first num frames to be skipped. Those frames are
written to the YUV output stream unfiltered.
-f: "Fast" filtering. The threshold-based averaging is not done;
instead a simple mean is calculated, much like what happens when
not enough values in the radius are within the threshold.
-w num: In fast mode, the weight to assign the current value, relative
to the values within the radius. Default is 8, just like in
the threshold-based version when not enough values are within the
threshold.
Note that certain combinations of radius/weight have been optimized
to be even faster -- radius 1 and weight 2.667, radius 1 and weight
8, and radius 2 and weight 8.
