Another master merge into the zoom buffer branch

configure.ac

doc/RTD/source/ExternalPotentials/index.rst

doc/RTD/source/SubgridModels/Basic/index.rst

doc/RTD/source/SubgridModels/GEAR/sinks/params.rst

...vityTests/MWPotential2014_circularorbit/params_unit_1.yml

...vityTests/MWPotential2014_circularorbit/params_unit_2.yml

...atedGalaxy/IsolatedGalaxy_multi_component/GEAR/params.yml

...es/IsolatedGalaxy/IsolatedGalaxy_sink/isolated_galaxy.yml

examples/SinkParticles/HomogeneousBox/params.yml

...ples/SinkParticles/HomogeneousBoxSinkParticles/params.yml

examples/SinkParticles/PlummerSphere/params.yml

examples/SinkParticles/SingleSink/README

examples/SinkParticles/SingleSink/make_sink_ic.py

examples/SinkParticles/SingleSink/make_test_plots.py

examples/SinkParticles/SingleSink/params.yml

examples/parameter_example.yml

src/Makefile.am

src/active.h

src/black_holes/Default/black_holes_part.h

src/black_holes/EAGLE/black_holes_part.h