Merge branch 'master' into gadget2-part-update

examples/CosmoVolume/cosmoVolume.yml

examples/EAGLE_12/eagle_12.yml

examples/EAGLE_25/eagle_25.yml

examples/EAGLE_50/eagle_50.yml

examples/ExternalPointMass/externalPointMass.yml

examples/MultiTypes/multiTypes.yml

examples/SedovBlast/sedov.yml

examples/SodShock/sodShock.yml

examples/UniformBox/uniformBox.yml

examples/main.c

examples/parameter_example.yml

src/adiabatic_index.h

src/common_io.c

src/drift.h

src/engine.c

src/hydro/Default/hydro.h

src/hydro/Default/hydro_iact.h

src/hydro/Default/hydro_part.h

src/hydro/Gadget2/hydro.h

src/hydro/Minimal/hydro.h