Please add support for non-copiable but movable types to C++ parser

[Askar Safin]

Please, add support for non-copiable, but movable (I mean C++11 moving 
construstors and moving operator=) semantic values to C++ parser (to %define 
api.value.type variant, of course).

For example, it is very useful to have the following semantic type for 
expressions like 2 + 3 - 4:
class expr
{
public:
  enum class kind {num, plus, minus};
  kind k;
  int num;
  std::unique_ptr<expr> a;
  std::unique_ptr<expr> b;
};

But, unfortunately, unique_ptr member makes this types non-copiable, so 
currently this class cannot be used as semantic value.
(CC me if you want to answer)


==
Askar Safin
http://vk.com/safinaskar
Kazan, Russia