Added some extra isothermal eos flags in Gizmo/hydro.h. Made sure gpart mass is updated when conserved mass changes. Fixed a number of possible issues with the isothermal Riemann solver.

Particle velocities are now correct. Period. Noh still does not work properly, but increasing resolution helps (so it is probably just a resolution issue).

Added some extra vacuum checks. Made sure isothermal Riemann solver crashes on vacuum (since isothermal vacuum cannot exist). Changed force.v_full to v instead of v_full and tried to explain why. Still have a problem with dt in acceleration computation which needs to be solved; will do this tomorrow.

Improved initial density guess in isothermal Riemann solver, which leads to (faster) convergence. Added some extra isothermal eos flags in Gizmo hydro.h. Temporarily disabled primitive variable drift and changed the way the actual particle movement is calculated.

Added some extra checks to correctly handle vacuum + some debug checks. 2D Noh test now seems to work with moving particles.

Cleaned up GIZMO gravity a bit. Still doesn't work. Added a gradient interpolation limiter that should solve the Noh problem.

Streamlined GIZMO_FIX_PARTICLES usage (tried to add parameter, but this does not work, as space_init has no access to the hydro_properties). Moved conserved variable initialization to hydro_first_init_part, and removed it from hydro_convert_quantities. Added some sanity checks to maintain positive density and pressure.

Cleaned up Gizmo fixes. Added a hydro_timestep_extra method and added an empty version for all hydro schemes.

Upgraded version number to reflect correct treatment of hydro in multi-dt and MPI as well as the inclusion of star particles.

Timestep order

This is my last batch of changes regarding time integration.
 
 - Additional checks here and there that the particles are synchronized. Especially gpart.
 - Re-arranged the time-step sequence and simplified the logic in engine_step().
 - Moved the decision of repartitioning from the main() to engine_step().

The re-arrangement of the time-step sequence allows for perfect energy conservation even when we rebuild, repartition or dump snapshots. Previously that was not the case as a spurious drift had to be introduced. 

See merge request !314

Properties of the self-gravity scheme are now read from the YAML file. They are printed to stdout and to snapshots.

Properties of the self-gravity scheme are now read from the YAML file. They are printed to stdout and to snapshots.