Add $$SET-TEMP$$ to image file macros (Suggestion)

For programs like PI’s WBPP, as well as human sorting of files, it is useful to have the cooler temperature in the file name. The actual current temperature, however, varies in fractions of degrees, and makes the current sensor temperature macro less than ideal (though it may be important as well and I do not suggest changing it).

The FITS header has a SET-TEMP; could we get a $$SET-TEMP$$ as well to name files accordingly.