Use RELATIVISTIC velocity convention instead of RADIO #17
Description
To be more precise, it would be better to use the relativistic convention where possible when converting velocities to frequencies. In particular for when the wide-bandwidth SKARAB spectra are used. This is because the further we get from the central frequency, the more velocity-channels will differ (assuming constant frequency-spaced channels). If the v_obs is calculated from astropy, then one of the few instances where this conversion is done is
line 454 in discosscan.py for the spectral resolution.
obs.head.spe.vres = - (self.freq_resolution / self.central_frequency) * CLIGHT
Formula for the relativistic vel resolution can be found on https://www.gb.nrao.edu/~fghigo/gbtdoc/doppler.html
Alternatively, this can be implemented allowing the user to pick the velocity convention.