Read-only flag on output images

In principle, every image from the CCD astronomical camera is unique. No repeating of heaven's mysteries is possible. Therefore, the utilities of nightview package creates every saved image as read-only by default. (Technically the unmask mode is set to 444 on Unix systems.) There is no switch for overwriting of this feature except patching and re-compilation of sources. If you can rewrite or delete your data (NOT RECOMMENDED), use chmod command for this purpose.

I was added this feature after unfortunately removing all of my images of the 1998WT24 asteroid, BL Lac observations and time series of SAX xxxx+xxx. Please, be careful.