migrate the C++ _<name> modules directly into the dune namespace

This allows them to be loaded without loading the corresponding Python
mdoule, avoiding circular dependencies.

CMakeLists.txt

@@ -8,5 +8,3 @@ add_python_targets(common
   pickle
   project
 )
-
-dune_add_pybind11_module(NAME _common)

__init__.py

@@ -21,10 +21,10 @@ try:
 except ImportError:
     logger.info('mpi4py not found, MPI not initialized')
 
-from ._common import *
+from .._common import *
 from .deprecated import DeprecatedObject
 
-from ..grid._grid import CommunicationDirection, DataType, InterfaceType, Marker, OutputType, PartitionType, reader
+from .._grid import CommunicationDirection, DataType, InterfaceType, Marker, OutputType, PartitionType, reader
 CommunicationDirection = DeprecatedObject(CommunicationDirection, "dune.common.CommunicationDirection is deprecated, use dune.grid.CommunicationDirection instead")
 DataType = DeprecatedObject(DataType, "dune.common.DataType is deprecated, use dune.grid.DataType instead")
 InterfaceType = DeprecatedObject(InterfaceType, "dune.common.Interface is deprecated, use dune.grid.InterfaceType instead")

_common.cc

-// -*- tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
-// vi: set et ts=4 sw=2 sts=2:
-#include <config.h>
-
-#include <utility>
-
-#include <dune/common/hybridutilities.hh>
-#include <dune/python/common/dynmatrix.hh>
-#include <dune/python/common/dynvector.hh>
-#include <dune/python/common/fmatrix.hh>
-#include <dune/python/common/fvector.hh>
-#include <dune/python/common/mpihelper.hh>
-
-#include <dune/python/pybind11/pybind11.h>
-#include <dune/python/pybind11/stl.h>
-
-PYBIND11_MODULE( _common, module )
-{
-  Dune::Python::addToTypeRegistry<double>(Dune::Python::GenerateTypeName("double"));
-  Dune::Python::addToTypeRegistry<int>(Dune::Python::GenerateTypeName("int"));
-  Dune::Python::addToTypeRegistry<std::size_t>(Dune::Python::GenerateTypeName("std::size_t"));
-
-  Dune::Python::registerFieldVector<double>(module, std::make_integer_sequence<int, 10>());
-
-  Dune::Hybrid::forEach( std::make_integer_sequence< int, 5 >(), [ module ] ( auto rows ) {
-      Dune::Hybrid::forEach( std::make_integer_sequence< int, 5 >(), [ module ] ( auto cols ) {
-        Dune::Python::registerFieldMatrix< double, decltype(rows)::value, cols >( module );
-      } );
-    } );
-
-  Dune::Python::registerDynamicVector<double>(module);
-  Dune::Python::registerDynamicMatrix<double>(module);
-
-  int argc = 0;
-  char **argv = NULL;
-  Dune::MPIHelper::instance(argc,argv);
-  Dune::Python::registerCollectiveCommunication(module);
-}