Merge branch 'master' into Self_gravity_BH

examples/main.c

src/cell.c

src/cell.h

src/common_io.c

src/debug.c

src/debug.h

src/engine.c

src/gravity/Default/gravity_debug.h

src/gravity/Default/gravity_io.h

src/gravity/Default/gravity_part.h

src/hydro/Default/hydro_debug.h

src/hydro/Gadget2/hydro_debug.h

src/hydro/Minimal/hydro_debug.h

src/part.c

src/part.h

src/runner.c

src/space.c

src/tools.c

src/tools.h