Make _x,_y_,_z parameters the arrays they should have always been

examples/CoolingHalo/cooling_halo.yml

examples/CoolingHaloWithSpin/cooling_halo.yml

examples/ExternalPointMass/externalPointMass.yml

examples/HydrostaticHalo/hydrostatic.yml

examples/IsothermalPotential/isothermal.yml

examples/KeplerianRing/keplerian_ring.yml

examples/KeplerianRing/write_gadget.py

examples/MultiTypes/multiTypes.yml

examples/SodShock_3D/sodShock.yml

examples/parameter_example.yml

src/potential/isothermal/potential.h

src/potential/point_mass/potential.h

src/potential/point_mass_ring/potential.h

src/potential/point_mass_softened/potential.h

src/space.c