change length or size specifiers in APIs from int to long

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

array/array_cats.c

@@ -0,0 +1,6 @@
+#include "array.h"
+#include "str.h"
+
+void array_cats(array* to,const char* from) {
+  array_catb(to,from,strlen(from));
+}