Support Non-LTE molecular radiative transfer codes

[migueldvb]

We should add support to non-LTE codes to infer physical and chemical parameters such as temperature, density, and production rates from spectroscopic observations. A python interface to run RADEX models has been developed and could be called from sbpy. The RADEX code is written in fortran and also has a command line interface. Wrapper functions in python would require using numpy.f2py to provide a connection with the fortran code.

https://personal.sron.nl/~vdtak/radex/index.shtml https://github.com/keflavich/pyradex

[gianninapr]

See #189