Add docs, move over to newer functional interface

meshmode/interop/firedrake/__init__.py

meshmode/interop/firedrake/connection.py

meshmode/interop/firedrake/function.py

meshmode/interop/firedrake/function_space.py

meshmode/interop/firedrake/function_space_coordless.py

meshmode/interop/firedrake/function_space_shared_data.py

meshmode/interop/firedrake/mesh.py

meshmode/interop/firedrake/mesh_geometry.py

meshmode/interop/firedrake/mesh_topology.py