Added placeholder for the to implement functions in the documentation

doc/wrappers.rst

@@ -623,6 +623,22 @@ Functions
 
    Returns the identifier of the target of association *ID* in model *model_name*.
 
+.. function:: service_register(name, function)
+
+.. function:: service_stop()
+
+.. function:: service_get(port)
+
+.. function:: service_set(port, value)
+
+.. function:: user_password(user, password)
+
+.. function:: transformation_read_signature(transformation)
+
+.. function:: element_list_nice(model_name)
+
+.. function:: connections_between(model_name, source_element, target_element)
+
 Exceptions
 ^^^^^^^^^^