Merge branch 'master' into io_unit_conversion

examples/main.c

examples/mkplots.m

src/Makefile.am

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_debug.h

src/gravity/Default/gravity_part.h

src/hydro/Default/hydro_debug.h

src/hydro/Default/hydro_io.h

src/hydro/Gadget2/hydro_debug.h

src/hydro/Gadget2/hydro_io.h

src/hydro/Minimal/hydro_debug.h

src/hydro/Minimal/hydro_io.h

src/parallel_io.c

src/parallel_io.h