Gear star formation split

examples/main.c

src/cell.c

src/cell.h

src/engine.h

src/runner_others.c

src/space.c

src/space.h

src/star_formation/EAGLE/star_formation.h

src/star_formation/GEAR/star_formation.h

src/star_formation/GEAR/star_formation_io.h

src/star_formation/GEAR/star_formation_struct.h

src/star_formation/QLA/star_formation.h

src/star_formation/none/star_formation.h

src/stars/GEAR/stars_io.h

src/stars/GEAR/stars_part.h