Added a branching function for dopair_subset, to switch between naive, serial and vectorised versions.

Make the hydro schemes compute the dirfted velocities themselves when collecting statistics.

See merge request !474

Skip pi particles that are not within range of any particle in cj. Face on pairs go 1.94x faster than serial

Removed the now obsolete checks that all correct tasks are active. Will need to be re-done correctly.

Add a SWIFT_DEVELOP_MODE flag to enable development code options

Closes #391

See merge request !473

Just uses abort() instead of exit() in non-MPI code

Compress hdf5 files and perform same tests with MPI.

See merge request !468

Kick1 update

See merge request !472

In kick1 after all is done, update the part's acceleration to include the gpart acceleration. This allows the hydro drift to use the correct accelerations for hydro predictions.

Added some extra sensibility checks to primitive variable drift.

See merge request !471

Also activate the gradient self and pair tasks in engine_marktasks() when running with the extra hydro loop

Restore correct dependencies between force loop and kick task when the extra hydro loop is activated.

Update cooling grackle

See merge request !469

Subpair density vectorised now runs fine with Sedov Blast and EAGLE_6 examples with sorted interactions.