Renamed StackReslicer into Tiler, made it capable to save in arbitrary
files formats as supported by ImageIO and made tile coordinates
freely formattable by a format string
added Downsampler class, n-d ImgLib2 based 1/2 averaging
fixed Downsampler.average to divide after accumulating
Tiler: fixed several bugs, enabled range selection for tile export,
added convenience calls with default parameters, added pyramid generator