Improve modularity, introduce arena_create()

test.c

@@ -2,13 +2,12 @@
 #include <stdlib.h>
 
 #ifdef DEBUG
-#define malloc(n) (printf("%s:%d:%s: malloc(%ld)\n",\
-            __FILE__, __LINE__, __func__, (n)), malloc((n)));
+#define realloc(p, s) (printf("%s:%d:%s: realloc(%p, %lu)\n",\
+            __FILE__, __LINE__, __func__, (p), (s)), realloc((p), (s)));
 #define free(p)   (printf("%s:%d:%s: free(%p)\n",\
             __FILE__, __LINE__, __func__, (p)), free((p)));
 #endif // DEBUG
 
-#define ARENA_MIN_CAPACITY 400
 #define ARENA_IMPLEMENTATION
 #include "arena.h"