moved get_direction from *_input.cc to input.h

src/input.h

@@ -1,5 +1,6 @@
 #ifndef __INPUT_H__
 #define __INPUT_H__
+#include <string>
 #include "constants.h"
 
 class input {
@@ -8,4 +9,7 @@ public:
         virtual game_command get_command() = 0;
 };
 
+game_command get_direction(std::string &str, const char *COMMANDS[],
+                           const int COMMANDS_CNT);
+
 #endif