made bin_up() function to compute q25,50,75 percentiles and bin centers for a given quantity like S/N using something like gmag to bin by, updated plot_SN() to plot flux/sigma instead of mag/sigma
made bin_up() function to compute q25,50,75 percentiles and bin centers for a given quantity like S/N using something like gmag to bin by, updated plot_SN() to plot flux/sigma instead of mag/sigma

legacysurvey/legacypipe,legacysurvey/legacypipe