Merge remote-tracking branch 'origin/master' into mark_tasks_in_drift2

examples/ExternalPointMass/run.sh

examples/IsothermalPotential/GravityOnly/README

src/cell.c

src/cell.h

src/engine.c

src/hydro/Gizmo/hydro.h

src/hydro/PressureEntropy/hydro.h

src/hydro/PressureEntropy/hydro_iact.h

src/minmax.h

src/riemann.h

src/riemann/riemann_exact_isothermal.h

src/riemann/riemann_hllc.h

src/riemann/riemann_trrs.h

src/runner.c

src/scheduler.c

src/space.c

src/space.h

src/task.c

src/task.h

theory/SPH/Flavours/sph_flavours.tex