Change mp_method_t.name from const char * to qstr.

Addresses issue #377.
diff --git a/py/obj.h b/py/obj.h
index 7c3ef8c..1c22e95 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -96,7 +96,7 @@
 typedef bool (*mp_store_item_fun_t)(mp_obj_t self_in, mp_obj_t index, mp_obj_t value); // return true if store succeeded
 
 typedef struct _mp_method_t {
-    const char *name;
+    qstr name;
     mp_const_obj_t fun;
 } mp_method_t;