Add to_int(int) and similar overloads

* This is so that `to_int` `to_char` `to_long` and similar work not
   only with strings but also with built-in types

include/chaiscript/dispatchkit/bootstrap.hpp

@@ -144,6 +144,7 @@ namespace chaiscript
       construct_pod<T>(name, m);
 
       m.add(fun(&parse_string<T>), "to_" + name);
+      m.add(fun([](const T t){ return t; }), "to_" + name);
     }