Implement stars sort

examples/DwarfGalaxy/run.sh

src/active.h

src/cell.c

src/cell.h

src/drift.h

src/engine.c

src/engine_maketasks.c

src/engine_marktasks.c

src/runner.c

src/runner.h

src/runner_doiact_stars.h

src/scheduler.c

src/space.c

src/stars/Default/stars_part.h

src/task.c

src/task.h

src/timers.c

src/timers.h

tests/test125cells.c

tests/test27cells.c