Also updated the Pressure-Entropy SPH scheme to use the new definition of the number of neighbours and its derivative. Back to correct results.

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet for AVX-512 vectors.

Conflicts:
	src/hydro/Gadget2/hydro_iact.h

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

Moved around the energy gravity update so that it uses the old momentum. Removed a superfluous time step in mflux.

Fixed bug in signal velocity computation. Added relative velocity of fluid w.r.t. particle velocity to timestep criterion.

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet for AVX-512 vectors.

Conflicts:
	src/hydro/Gadget2/hydro_iact.h

Use intrinsics for vector operations as arithmetic overloading is not supported by the Intel compiler yet for AVX-512 vectors.

Updated the way we converge towards the smoothing length. We now use a Newton-Raphson scheme. This applies to the Gadget-2 scheme.

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

Correctly initialise the signal velocity of the SPH particles in the Minimal and Pressure-Entropy cases.

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

Removed un-masked versions of the force interaction and incorporated them in runner_nonsym_force_2_vec with an if statement based on a hard coded mask_cond variable.

Initialize the signal velocity to be the particle's sound-speed. Prevents divisions by zero in cases where a particle has 0 neighbours.

Created a typedef for a mask object to abstract the mask creation away from the user and placed it in vector.h.