renamed display to output

src/game.h

@@ -2,7 +2,7 @@
 #define __GAME_H__
 #include <memory>
 #include <vector>
-#include "display.h"
+#include "output.h"
 #include "input.h"
 #include "rng.h"
 #include "characters.h"
@@ -22,7 +22,7 @@ private:
         const feature enabled_features;
 
         input   *in;
-        display *out;
+        output *out;
         RNG     *rng;
 
         unsigned int curr_turn;
@@ -42,7 +42,7 @@ public:
         game(const enum race starting_race,
              const feature enabled_features,
              input   *new_in,
-             display *new_out,
+             output *new_out,
              RNG     *new_rng);
         game_result run();
         size_t get_curr_level() const;