Patch: Add arena constructor to memory.h

src/memory.h

@@ -1,7 +1,6 @@
 #ifndef MEMORY_H
 #define MEMORY_H
 
-
 #ifndef MEM_ARENA_MAX_CAP
 #define MEM_ARENA_MAX_CAP 1024 * 1024
 #endif
@@ -20,16 +19,20 @@ struct Backend
   size_t cap;
 };
 
+#define BACKEND_CONST {NULL, NULL, 0, 0}
+
 struct Arena
 {
   void* mem;
   void* last;
   size_t len;
   size_t cap;
-  void* next;
+  void* next; //TODO
   struct Backend* b;
 };
 
+#define ARENA_CONST {NULL, NULL, 0, 0, NULL}
+
 typedef struct Backend Backend;
 typedef struct Arena Arena;