added --dostack
 * the --dostack option allows you to construct a stacked image comprising
   all non-template epochs in a single filter. Useful for making a deep
   image with multiple SN epochs in order to pin down the SN position.
 * this stage is run by default when the --doall option is set.
major upgrade to single star registration
  * principal improvement is in the way sources are located in single-star images
  * several new steps ensure that we locate the desired star, and the addition of
    a centroid function assures that we avoid catastrophic errors in source positioning.
  -- This version has been successfully tested on a limted set of WFC3-IR images --
added --verboselevel option
  * for dialing the verbosity up to 11.