change length or size specifiers in APIs from int to long

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

array/array_cate.c

@@ -0,0 +1,9 @@
+#include "array.h"
+
+void array_cate(array* to,const array* const from,int64 pos,int64 stop) {
+  if (pos<0 || stop<pos) {
+    array_fail(to);
+    return;
+  }
+  array_catb(to,from->p+pos,stop-pos);
+}