Copy docs into Zeek repo directly

This is based on commit 2731def9159247e6da8a3191783c89683363689c from the
zeek-docs repo.

doc/scripting/data_struct_vector_iter.zeek

@@ -0,0 +1,7 @@
+event zeek_init()
+    {
+    local addr_vector: vector of addr = vector(1.2.3.4, 2.3.4.5, 3.4.5.6);
+
+    for ( i in addr_vector )
+        print mask_addr(addr_vector[i], 18);
+    }