Add barotropic EoS
Add barotropic EoS that is used in some MHD problems.
Todo:
-
Add reference to the paper where this is taken from, -
Fix the few equations labelled as "IS THIS CORRECT", -
Fix the Doxygen comments to have the correct equations. -
Fix the example/parameter_examples.yml file to have a description of the two parameters.
Edited by Matthieu Schaller