Merge remote-tracking branch 'origin/master' into faster_rebuilds

examples/Vacuum_3D/vacuum.yml

examples/main.c

examples/parameter_example.yml

m4/ax_cc_maxopt.m4

m4/ax_gcc_archflag.m4

src/Makefile.am

src/align.h

src/atomic.h

src/cell.c

src/chemistry.h

src/chemistry/EAGLE/chemistry.h

src/chemistry/EAGLE/chemistry_iact.h

src/chemistry/gear/chemistry.h

src/chemistry/gear/chemistry_iact.h

src/chemistry/gear/chemistry_io.h

src/chemistry/gear/chemistry_struct.h

src/chemistry/none/chemistry.h

src/chemistry/none/chemistry_iact.h

src/clocks.c

src/clocks.h