Shift the particle positions in the cache by cj instead of ci to prevent loss of accuracy when periodic boundary conditions occur. Also added debugging checks to make sure that particles are shifed correctly.

Conflicts:
	src/runner_doiact.h

Cache auto vec

Auto-vectorise populating the cache with hints to the compiler and `restrict` keyword.

See merge request !404

Correct the use of rshift to reduce the number of distance calculations.

Applies `rshift` (boundary conditions) correctly in `DOPAIR1` + `DOPAIR2` to reduce the number of spurious distance calculations.

See merge request !403

Avx512 fixes

* Adds a generic mask, `mask_t`, for each instruction set (AVX, AVX2, AVX512)
* Removes testPair and testPairPerturbed which are superseded by test27cells and test27cellsPerturbed
* Adds testActivePair that computes the density between a pair of cells in various configurations of active particles (face, edge, corner)
* Replaces all arithmetic vector operations to support AVX512 as there is no compiler support to overload them
* Computes max_index_i[] for each particle in runner_dopair1_density_vec to follow ParCo paper
* testInteractions now calls correct vectorised density particle interactions and is run as a part of the test suite
* Solves #327


See merge request !396

Updated tolerances because the command line argument, -p, is now used in test27cells.c to perturb the smoothing length and not just the default value of 1.1f.

Added extra test case to test27cells.sh and test27cellsPerturbed.sh to perturb the smoothing lengths further to pick up extra edge cases.

Fix scheduler steal policy

Set `scheduler` steal policy from `engine` policy. 

Solves #347.

See merge request !399

Conflicts:
	tests/testPair.c

Yamling

Warn when overriding parameters from the command-line.

See merge request !402

No need to explicitly activate the drift_part task in engine_marktask()
All the required drifts will be activated when we loop over the density pairs and call `cell_activate_drift_part()`. 

See merge request !401

Correct use of caches in the self-PP gravity task. Make sure we can run without vectorization. Make sure we can run without hydro.

Bug fix in the test suite. Move the gravity leaf P-P interaction in the frame of the cells. Use a cache for the self P-P interaction.



See merge request !400