Merge branch 'master' into mpi-communication

contrib/maxima/maxwellrectcav3d.mac

examples/advection/var-velocity.py

examples/advection/weak.py

examples/maxwell/analytic_solutions.py

examples/maxwell/cavities.py

examples/wave/var-propagation-speed.py

examples/wave/wave-min.py

grudge/__init__.py

grudge/discretization.py

grudge/execution.py

grudge/models/em.py

grudge/shortcuts.py

grudge/symbolic/compiler.py

grudge/symbolic/mappers/__init__.py

grudge/symbolic/operators.py

grudge/symbolic/primitives.py

grudge/tools.py

test/test_grudge.py