Modify equations to include supersonic flows

This paper and the subsequent EBTEL-3 code provide a modification of the EBTEL model to include a more careful treatment of the velocities by including the kinetic energy terms in the derivation of the EBTEL equations. We should rederive the EBTEL equations again, starting with the two-fluid hydrodynamic equations and applying the methodology of the aforementioned paper such that our model can include two-fluid effects, area expansion, and a more proper treatment of the velocities.