Other scripts:
- DSLR_preprocessing_opt.ssf. Preprocess images with dark optimization: added 01/24/2019.
- DSLR_startrail.ssf. Preprocess images and build a star-trail: added 02/12/2019.
- DSLR_preprocessing_opt_diff_biases.ssf. Preprocess images with biases at same ISO of darks and other biases with same ISO of flats (generally the lowest): added 03/02/2019.