Use pybind11 as binding framework

This commit changes the api for the Schedule class, the various time related
methods now return datetime.datetime instances instead of datetime.data.

sunbeam/group.cpp

@@ -1,20 +1,19 @@
 #include <opm/parser/eclipse/EclipseState/Schedule/Group.hpp>
-
+#include <pybind11/stl.h>
 #include "sunbeam.hpp"
 
 
 namespace {
 
-    py::list wellnames( const Group& g, size_t timestep ) {
-        return iterable_to_pylist( g.getWells( timestep )  );
+  const std::set<std::string> wellnames( const Group& g, size_t timestep ) {
+        return g.getWells( timestep );
     }
 }
 
-void sunbeam::export_Group() {
+void sunbeam::export_Group(py::module& module) {
 
-    py::class_< Group >( "Group", py::no_init )
-        .add_property( "name", mkcopy( &Group::name ) )
-        .def( "_wellnames", &wellnames )
-        ;
+  py::class_< Group >( module, "Group")
+    .def_property_readonly( "name", &Group::name)
+    .def( "_wellnames", &wellnames );
 
 }