Replaced builtin store function with a new syntax

lib/mem/alloc_unix.q

@@ -7,6 +7,6 @@ alloc(length int) -> []byte {
 		return x
 	}
 
-	store(x, 8, length)
+	[x] = length
 	return x + 8
 }

lib/mem/alloc_windows.q

@@ -5,7 +5,7 @@ alloc(length int) -> []byte {
 		return x
 	}
 
-	store(x, 8, length)
+	[x] = length
 	return x + 8
 }