Merge branch 'gear_star_formation' into 'master'

configure.ac

src/Makefile.am

src/runner.c

src/runner_doiact.h

src/space.c

src/star_formation.h

src/star_formation/EAGLE/star_formation.h

src/star_formation/EAGLE/star_formation_iact.h

src/star_formation/GEAR/star_formation.h

src/star_formation/GEAR/star_formation_iact.h

src/star_formation/GEAR/star_formation_io.h

src/star_formation/GEAR/star_formation_struct.h

src/star_formation/none/star_formation.h

src/star_formation/none/star_formation_iact.h

src/star_formation_iact.h

src/star_formation_io.h

src/star_formation_struct.h

src/tools.c