Applied formatting rules to all files

examples/main.c

src/cell.c

src/cell.h

src/common_io.c

src/debug.c

src/debug.h

src/engine.c

src/engine.h

src/gravity/Default/gravity.h

src/gravity/Default/gravity_part.h

src/hydro/Default/hydro.h

src/hydro/Default/hydro_part.h

src/hydro/Gadget2/hydro.h

src/hydro/Gadget2/hydro_iact.h

src/hydro/Gadget2/hydro_part.h

src/parallel_io.c

src/part.c

src/part.h

src/queue.c

src/queue.h