Add code generation for doubly linked list

codegen/dbl_list/snippets/list_push_front

@@ -0,0 +1,21 @@
+  if (!list || !node || !(node->string)) {{
+    return;
+  }}
+
+  {T}List node_list = {Tlower}_node_to_list(node);
+
+  if (list->node_count == 0) {{
+    *list = node_list;
+    return;
+  }}
+
+  list->total_size += node_list.total_size;
+  list->node_count += node_list.node_count;
+
+  {T}Node *first = list->first;
+  if (first) {{
+    first->prev = node_list.last;
+  }}
+
+  list->first          = node_list.first;
+  node_list.last->next = first;