change length or size specifiers in APIs from int to long

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

array/array_cat0.c

@@ -0,0 +1,6 @@
+#include "array.h"
+
+void array_cat0(array* to) {
+  static char zero;
+  array_catb(to,&zero,1);
+}