Added reference result for interacting blast waves. Added 2D and 3D spherical vacuum expansion test. Disabled pathological particle configuration errors in GIZMO to make 3D vacuum test work.

When compiling with the iosthermal equation of state, read the constant thermal energy from the YAML file.

All gpart now find all of their interactions following correct boundary condition check in runner_do_grav_long_range()

Fixed the gravity bugs reported in #363. Need to find a good rebuild criterion for gravity-only runs.

Partially restored old time step criterion. Isolated flux limiter into a separate file and made it configurable. Removed some superfluous gravity variables.

Updated the hydrodstatic disc patch example to use a longer slab in z and the correct internal energy.

Disabled GIZMO particle steering for vacuum particles. Disabled warning messages for unphysical values and pathological configurations.

Implemented the changes in ls that prevent gizmo crashes in cases where the mesh is seriously distorted

Fixed wrong box size in 2D Sod shock that caused SHADOWFAX_SPH to crash. Added flag in const.h to enable or disable cell motion steering. Made sure cell centroids have all their coordinates initialized.

Fixed bug in 2D Voronoi algorithm. Sod shock now works (with fixed cells). Moved gradient and slope limiter defines for SHADOWFAX_SPH to const.h.

Cleaned up 1D Voronoi algorithm some more. Added SHADOWFAX_TOTAL_ENERGY flag and support for an isothermal EoS.

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.

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.