Reorganise the code

src/mem/arena/mem_arena.h

@@ -0,0 +1,23 @@
+#ifndef MEM_ARENA_H
+#define MEM_ARENA_H
+
+#include "aliases.h"
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif // __cplusplus
+
+typedef struct growing_arena Arena;
+
+bool wapp_mem_arena_init(Arena **arena, u64 base_capacity);
+void *wapp_mem_arena_alloc(Arena *arena, u64 size);
+void *wapp_mem_arena_alloc_aligned(Arena *arena, u64 size, u64 alignment);
+void wapp_mem_arena_clear(Arena *arena);
+void wapp_mem_arena_destroy(Arena **arena);
+
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
+#endif // !MEM_ARENA_H