change Export keybinding to Alt-P

Program.cs

@@ -623,6 +623,7 @@ public class Game : GameWindow {
     KeyboardState input = KeyboardState;
 
     bool shiftIsDown = input.IsKeyDown(Keys.LeftShift) || input.IsKeyDown(Keys.RightShift);
+    bool altIsDown = input.IsKeyDown(Keys.LeftAlt) || input.IsKeyDown(Keys.RightAlt);
     bool ctrlIsDown = input.IsKeyDown(Keys.LeftControl) || input.IsKeyDown(Keys.RightControl);
 
     // FIXME: add a confirm dialog before closing. (Also for the window-close button.)
@@ -690,7 +691,7 @@ public class Game : GameWindow {
       photoIndex -= 5;
     }
 
-    if (input.IsKeyPressed(Keys.P) && shiftIsDown) {
+    if (input.IsKeyPressed(Keys.P) && altIsDown) {
       ExportPhotos();
     }