macroturbulence

[ajwheeler]

The solar macroturbulence is about 3.5 km/s (https://ui.adsabs.harvard.edu/abs/2014MNRAS.444.3592D)

This isn't negligible for high resolution data, so Korg should have a way of dealing with it. It would make sense to tackle this at the same time as #273, though there is less reason to do this for macrotubulence since the velocity kernels are pretty ad-hoc.

It probably makes sense to support at least radial-tangential and gaussian macroturbulence. Possibly anisotropically.

Related #259.