Fix alloc.c as per #386, define INVALID_ constants and rename malloc to alloc as per #325

Some of the INVALID_ are likely erroneously placed, due to lack of documentation

src/egg_hatch.c

@@ -17,7 +17,7 @@
 #include "menu.h"
 #include "trig.h"
 #include "random.h"
-#include "malloc.h"
+#include "alloc.h"
 #include "dma3.h"
 #include "gpu_regs.h"
 #include "bg.h"