Added more in depth timers for interaction functions and added macros to choose which versioin of DOSELF1 to use.

Changed scenario to a test particle at the center of a unit sphere. The serial results are now compared against the vectorised results using the compare functions and differences are flagged.

Added functions to compare particles' properties and return an error if they differ more than the provided accuracy.

Replaced all vector reciprocals with macros and fixed a bug in the non-sym and sym vector force interactions. Missing grad-h multiply in the sph-term.

Added more vector intrinsics for AVX512 and support for left-packing vectors in multiple instruction sets.

Scheduler activate root

Re-set the task waits on activation, saves a loop over the tasks in `scheduler_start`.

See merge request !282

Added debugging checks to the pair and self tasks to make sure cells have been drifted to this point before they get updated.

Added debugging checks to the pair and self tasks to make sure cells have been drifted to this point before they get updated.

Added an (expensive) debugging check to verify that all cells have been drifted to the current point in time before a rebuild or a repartition.

Add -funroll-loops as a standard GCC optimization

SWIFT is faster with this.

Fixes #244.

See merge request !283