initial export BCRSMatrix to Python

CMakeLists.txt

+add_python_targets(istl
+  __init__
+)
+
+add_library(_istl SHARED _istl.cc)
+set_target_properties(_istl PROPERTIES PREFIX "")

__init__.py

+from ._istl import *

_istl.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 <dune/common/fmatrix.hh>
+
+#include <dune/istl/bcrsmatrix.hh>
+
+#include <dune/corepy/istl/bcrsmatrix.hh>
+
+#include <dune/corepy/pybind11/pybind11.h>
+
+PYBIND11_PLUGIN(_istl)
+{
+  pybind11::module module( "_istl" );
+
+  Dune::CorePy::registerBCRSMatrix< Dune::BCRSMatrix< Dune::FieldMatrix< double, 1, 1 > > >( module );
+
+  return module.ptr();
+}