Merge branch 'master' into add_particles

configure.ac

doc/RTD/source/Cooling/index.rst

doc/RTD/source/InitialConditions/index.rst

doc/RTD/source/ParameterFiles/index.rst

doc/RTD/source/VELOCIraptorInterface/index.rst

doc/RTD/source/VELOCIraptorInterface/output.rst

doc/RTD/source/VELOCIraptorInterface/whatis.rst

examples/DwarfGalaxy/run.sh

examples/ExternalPointMass/energy_plot.py

examples/ExternalPointMass/makeIC.py

examples/main.c

src/Makefile.am

src/active.h

src/cell.c

src/cell.h

src/drift.h

src/engine.c

src/engine.h

src/engine_drift.c

src/engine_maketasks.c