find-xy-shell.py - save much more data about each arc, and about the central source,

+ We now save the RA, Dec offsets (x, y) as well as the offsets in frame of arc (X, Y)
+ We save the coordinates, distance from th1C, and PA of the central star
+ There is the option to fit the parabola to all arc points, not just the closest 3 to the star