fits_warp: Warp catalogs and images to dedistort the effects of the ionosphere

fits_warp smoothly removes the distorting effect of the ionosphere and restores sources to their reference positions in both the catalog and image domain. Image warping uses pixel offsets derived from a catalog of cross-matched sources. Though initially written for low-frequency radio astronomy, fits_warp can be used to de-distort any image distorted by some vector field which is sampled by some sparse pierce-points.