Add code generation for doubly linked list

codegen/dbl_list/snippets/list_pop_front

@@ -0,0 +1,21 @@
+  {T}Node *output = NULL;
+
+  if (!list || list->node_count == 0) {{
+    goto RETURN_{Tupper}_LIST_POP_FRONT;
+  }}
+
+  output = list->first;
+
+  if (list->node_count == 1) {{
+    *list = ({T}List){{0}};
+    goto RETURN_{Tupper}_LIST_POP_FRONT;
+  }}
+
+  --(list->node_count);
+  list->total_size -= output->string->size;
+  list->first       = output->next;
+
+  output->prev = output->next = NULL;
+
+RETURN_{Tupper}_LIST_POP_FRONT:
+  return output;