Bug inside debug checks.

There was an extra `{` on line 637 of `runner_doiact_vec.c` that I missed because I never compiled debugging checks enabled. I also formatted the rest of the code, which messes up the diff in gitlab.

See merge request !413

Conflicts:
	src/runner_doiact_vec.c

Doself2 vectorisation

Implements:
* `runner_doself2_force_vec` a vectorised version of the `DOSELF2` for force interactions.
* Updates particle cache with properties needed for force interactions.
* Vectorised interaction functions for the force using 1 and 2 vectors, which are tested in `testInteractions.c`

See merge request !406

Changed call to part_is_active to new function. Also removed unnecessary load of v_hj in runner_doself2_vec.

Created a new function to check that a particle is active, without passing in a pointer to the engine.

Use getticks() to get enough randomness when enqueing tasks without owners.

How about this version ?

See merge request !411

Added cpuid for Kaby Lake processor and corresponding compilation flags.

Could you let me know whether this works ? I think I got the correct cpuid pattern for KabyLake...

See merge request !410

Make the expected number of tasks per cell a parameter.

Previously we had a max of 96, much smaller numbers will work depending on the job

See merge request !395

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.

Removed alternate version of doself2_vec that was slower than current version. Renamed some variables. Removed left-packing functions for force interactions as they are not used anymore.

Created new version of doself2_vec that computes force interaction on the fly, 2.1x faster than serial.

Replace calls to rand() by calls to rand_r() in the scheduler

Implements #302 using @d74ksy's changes. 

See merge request !405