Merge branch 'master' into metishostweights

.gitignore

configure.ac

doc/RTD/source/RadiativeTransfer/GEAR_RT.rst

examples/EAGLE_low_z/EAGLE_12/README

examples/EAGLE_low_z/EAGLE_12/eagle_12_rt_test.yml

examples/EAGLE_low_z/EAGLE_25/README

examples/EAGLE_low_z/EAGLE_25/eagle_25_rt_test.yml

examples/EAGLE_low_z/EAGLE_25/run_rt_test.sh

examples/RadiativeTransferTests/CoolingTest/plotSolution.py

examples/RadiativeTransferTests/RandomizedBox_3D/README

m4/ax_gcc_archflag.m4

src/active.h

src/cell_unskip.c

src/engine_maketasks.c

src/engine_marktasks.c

src/equation_of_state/planetary/hm80.h

src/riemann/riemann_exact.h

src/rt/GEAR/rt.h

src/rt/GEAR/rt_grackle_utils.h

src/rt/GEAR/rt_properties.h