Merge branch 'multi_softening' into 'master'

configure.ac

doc/RTD/source/InitialConditions/index.rst

doc/RTD/source/ParameterFiles/parameter_description.rst

doc/RTD/source/Snapshots/index.rst

examples/Cosmology/ConstantCosmoVolume/constant_volume.yml

examples/Cosmology/ZeldovichPancake_3D/zeldovichPancake.yml

examples/EAGLE_DMO_low_z/EAGLE_DMO_100/eagle_100.yml

examples/EAGLE_DMO_low_z/EAGLE_DMO_12/eagle_12.yml

examples/EAGLE_DMO_low_z/EAGLE_DMO_25/eagle_25.yml

examples/EAGLE_DMO_low_z/EAGLE_DMO_50/eagle_50.yml

examples/EAGLE_ICs/EAGLE_12/eagle_12.yml

examples/EAGLE_ICs/EAGLE_25/eagle_25.yml

examples/EAGLE_ICs/EAGLE_50/eagle_50.yml

examples/EAGLE_low_z/EAGLE_100/eagle_100.yml

examples/EAGLE_low_z/EAGLE_12/eagle_12.yml

examples/EAGLE_low_z/EAGLE_25/eagle_25.yml

examples/EAGLE_low_z/EAGLE_50/eagle_50.yml

examples/EAGLE_low_z/EAGLE_6/eagle_6.yml

examples/GiantImpacts/GiantImpact/uranus_1e6.yml

...atedGalaxy/IsolatedGalaxy_dmparticles/isolated_galaxy.yml