Add classes for event-handling

The new classes Event and EventSource can be used as a simple mechanism
for implementing event-based callbacks in the simulators.

opm/core/utility/Event_impl.hpp

@@ -0,0 +1,13 @@
+// Copyright (C) 2013 Uni Research AS
+// This file is licensed under the GNU General Public License v3.0
+
+#ifndef OPM_EVENT_HEADER_INCLUDED
+#error Do NOT include this file directly!
+#endif /* OPM_EVENT_HEADER_INCLUDED */
+
+template <typename T, void (T::*member)()> inline Event&
+Event::add (T& t) {
+    // wrap the member function in a std::function and add that
+    // notice the use of ref() to avoid invoking the copy constructor
+    return this->add (std::bind (member, std::ref(t)));
+}