change length or size specifiers in APIs from int to long

add array API (http://cr.yp.to/lib/array.html)

array/array_reset.c

@@ -0,0 +1,8 @@
+#include <stdlib.h>
+#include "array.h"
+
+void array_reset(array* x) {
+  if (x->p) free(x->p);
+  x->p=0;
+  x->allocated=x->initialized=0;
+}