[ruamoko] Implement default -describe method on Object

It returns [classname@address], which is probably a reasonable default.

ruamoko/lib/Object.r

@@ -1,5 +1,6 @@
 #include <Object.h>
 #include <AutoreleasePool.h>
+#include <string.h>
 
 static void link__obj_forward (void)
 {
@@ -367,4 +368,9 @@ typedef void arIMP(id, SEL, id);
 	return self;
 }
 
+- (string) describe
+{
+	return sprintf ("[%s@%p]", object_get_class_name (self), self);
+}
+
 @end