Async UCI options actions

Introduce 'on change' actions that are triggered as soon as
an UCI option is changed by the GUI. This allows to set hash
size before to start the game, helpful especially on very fast
TC and big TT size.

As a side effect remove the 'button' type option, that now
is managed as a 'check' type.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/ucioption.h

@@ -29,11 +29,14 @@ struct OptionsMap;
 
 /// UCIOption class implements an option as defined by UCI protocol
 class UCIOption {
+
+  typedef void (Fn)(UCIOption&);
+
 public:
   UCIOption() {} // Required by std::map::operator[]
-  UCIOption(const char* v);
-  UCIOption(bool v, std::string type = "check");
-  UCIOption(int v, int min, int max);
+  UCIOption(const char* v, Fn* = NULL);
+  UCIOption(bool v, Fn* = NULL);
+  UCIOption(int v, int min, int max, Fn* = NULL);
 
   void operator=(const std::string& v);
   void operator=(bool v) { *this = std::string(v ? "true" : "false"); }
@@ -54,6 +57,7 @@ private:
   std::string defaultValue, currentValue, type;
   int min, max;
   size_t idx;
+  Fn* on_change_action;
 };