Merge pull request #18 from alexfikl/py3-upgrades

doc/conf.py

examples/advection/surface.py

examples/advection/var-velocity.py

examples/advection/weak.py

examples/dagrt-fusion.py

examples/geometry.py

examples/maxwell/cavities.py

examples/wave/var-propagation-speed.py

examples/wave/wave-eager-mpi.py

examples/wave/wave-eager-var-velocity.py

examples/wave/wave-eager.py

examples/wave/wave-min-mpi.py

examples/wave/wave-min.py

grudge/__init__.py

grudge/discretization.py

grudge/dt_finding.py

grudge/eager.py

grudge/execution.py

grudge/function_registry.py

grudge/models/__init__.py