Castro 20.04

20.04

• A potential undefined flux from the HLL solver when using
  hybrid_riemann has been fixed (#823)

• The parameter castro.allow_small_energy has been removed. The
  code behavior is now similar to what it would have been with
  allow_small_energy == 0 (the internal energy can never be
  smaller than that allowed by small_temp). (#817)

• The BC interfaces have been merged and converted to a new FAB
  interface as part of the port to C++. (#819)

• All boundary fill interfaces other than hypfill and denfill have
  been removed. So, we no longer support overriding the boundary
  conditions for data other than State_Type. Radiation still has
  its own set of custom boundary conditions that can be accessed
  through the inputs file, as described in the docs. (#815)

• The conversion of the CTU hydrodynamics code to C++ continues.
  The Riemann solvers were converted to C++ (#801) and the
  hybrid momentum routines (#805), the PLM reconstruction (#814),
  the conversion of primitive to conserved variables (#804)

• We've changed how the backup for retries is done. Presently if
  use_retry is enabled we make a pre-emptive copy of the StateData
  right at the beginning of the timestep. Now we only backup when
  we detect that a retry is needed (#812)