TOneDReader.doDecode Method

We're going to examine rows from the middle outward, searching alternately above and below the middle, and farther out each time. rowStep is the number of rows between each successive attempt above and below the middle. So we'd scan row middle, then middle - rowStep, then middle + rowStep, then middle - (2 * rowStep), etc. rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily decided that moving up and down by about 1/16 of the image is pretty good; we try more of the image if "trying harder".