map: Add mp_map_dump() (#ifdef'ed) to be handy when debugging maps.
diff --git a/py/map.c b/py/map.c
index d424c27..301ea51 100644
--- a/py/map.c
+++ b/py/map.c
@@ -243,3 +243,17 @@
     set->used = 0;
     set->table = NULL;
 }
+
+#if DEBUG_PRINT
+void mp_map_dump(mp_map_t *map) {
+    for (int i = 0; i < map->alloc; i++) {
+        if (map->table[i].key != NULL) {
+            mp_obj_print(map->table[i].key, PRINT_REPR);
+        } else {
+            printf("(nil)");
+        }
+        printf(": %p\n", map->table[i].value);
+    }
+    printf("---\n");
+}
+#endif