Merge branch 'master' into gravity_multi_dt

INSTALL.swift

examples/BigCosmoVolume/makeIC.py

examples/CoolingHalo/makeIC.py

examples/CoolingHaloWithSpin/makeIC.py

examples/DiscPatch/GravityOnly/makeIC.py

examples/DiscPatch/HydroStatic/makeIC.py

examples/HydrostaticHalo/density_profile.py

examples/HydrostaticHalo/internal_energy_profile.py

examples/HydrostaticHalo/makeIC.py

examples/HydrostaticHalo/velocity_profile.py

examples/IsothermalPotential/makeIC.py

examples/Noh_3D/makeIC.py

examples/SineWavePotential_3D/plotSolution.py

src/space.c

src/task.c

tests/test125cells.c

tests/test27cells.c

tests/testPair.c