Flux calibration of BOSS spectra

[freddavies]

BOSS DR14 includes corrections to the flux calibration following this paper. But, in advance of ingesting the whole new data release (sans quasar catalog), those corrections for the DR12Q spectra are also available as a separate HDF5 file with instructions here.

Edit: Something I should point out, which I didn't realize before, is that the calibration corrections are more deeply embedded into the DR14 reduction process (e.g. applied on a per-exposure basis), so these DR12 corrections are not exactly equivalent to what is in DR14.