Implement cell_unskip_stars_tasks + format

examples/main.c

src/cell.c

src/cell.h

src/common_io.c

src/common_io.h

src/engine.c

src/engine.h

src/parallel_io.c

src/part_type.c

src/runner.c

src/runner_doiact_stars.h

src/scheduler.c

src/single_io.c

src/space.c

src/stars/Default/stars.h

src/stars/Default/stars_iact.h

src/stars/Default/stars_io.h

src/stars/Default/stars_part.h

src/task.c

src/tools.c