Merge branch 'master' into super_for_gravity

README

examples/Makefile.am

examples/main.c

examples/plot_scaling_results.py

src/cell.c

src/cell.h

src/engine.c

src/engine.h

src/kernel_hydro.h

src/parallel_io.c

src/runner.c

src/serial_io.c

src/single_io.c

src/space.c

tests/Makefile.am