Fix typos in the Tillotson sound speed

See merge request !725

Use the threadpool to populate the array of VELOCIraptor particles from the gparts in the interface.

Runs now initialise velociraptor correctly upon restart. When writing the last snapshot, invoke VR if that what asked for in the parameter file.

Minor documentation fixes; now compiles without warnings

See merge request !724

Velociraptor outputs

See merge request !721

Updated a_x tolerance for test125cellsPerturbed.sh.

See merge request !722

When running with VELOCIraptor, collect the DM particle in group for i/o alongside the regular gpart data.

In the vectorized cache construction, return 0 and an error message when not compiling with GADGET2-SPH.

Inhibit vec

Closes #481

See merge request !699