Merge branch 'particle_splitting' into 'master'

src/cooling/none/cooling.h

src/engine.c

src/engine.h

src/engine_split_particles.c

src/hydro_properties.c

src/hydro_properties.h

src/star_formation/EAGLE/star_formation.h

src/star_formation/EAGLE/star_formation_struct.h

src/star_formation/GEAR/star_formation.h

src/star_formation/none/star_formation.h

src/tracers/EAGLE/tracers.h

src/tracers/none/tracers.h

tools/analyse_runtime.py