Add support for specialized session interfaces

This patch introduces principal support for extending session interfaces
with specialized functionality in a clean way. For example, an 'Uart'
interface may implement the 'Terminal' interface but also offers
additional functions for setting the baud rate. A service that
implements the 'Uart' service will then automatically announce both the
'Uart' and 'Terminal' services.

base/include/util/meta.h

@@ -637,6 +637,11 @@ namespace Genode {
 			Overload_selector() { }
 		};
 
+		/**
+		 * Convert boolean value to type
+		 */
+		template <bool VALUE> struct Bool_to_type { enum { V = VALUE }; };
+
 	} /* namespace Meta */
 }