Swap MENU and APP_SWITCH shortcuts

Ctrl+s was mapped to MENU, while Ctrl+m was mapped to APP_SWITCH.

To avoid confusion, swap the shortcuts:
 - Ctrl+m like _M_enu
 - Ctrl+s like _S_witch

README.md

@@ -257,8 +257,8 @@ To run without installing:
  | resize window to remove black borders  | `Ctrl`+`x` \| _Double-click¹_ |
  | click on `HOME`                        | `Ctrl`+`h` \| _Middle-click_  |
  | click on `BACK`                        | `Ctrl`+`b` \| _Right-click²_  |
- | click on `APP_SWITCH`                  | `Ctrl`+`m`                    |
+ | click on `APP_SWITCH`                  | `Ctrl`+`s`                    |
- | click on `MENU`                        | `Ctrl`+`s`                    |
+ | click on `MENU`                        | `Ctrl`+`m`                    |
  | click on `VOLUME_UP`                   | `Ctrl`+`+`                    |
  | click on `VOLUME_DOWN`                 | `Ctrl`+`-`                    |
  | click on `POWER`                       | `Ctrl`+`p`                    |

app/src/inputmanager.c

@@ -180,10 +180,10 @@ void input_manager_process_key(struct input_manager *input_manager,
             case SDLK_BACKSPACE:
                 action_back(input_manager->controller);
                 return;
-            case SDLK_m:
+            case SDLK_s:
                 action_app_switch(input_manager->controller);
                 return;
-            case SDLK_s:
+            case SDLK_m:
                 action_menu(input_manager->controller);
                 return;
             case SDLK_p:

app/src/main.c

@@ -70,10 +70,10 @@ static void usage(const char *arg0) {
         "    Right-click (when screen is on)\n"
         "        click on BACK\n"
         "\n"
-        "    Ctrl+m\n"
+        "    Ctrl+s\n"
         "        click on APP_SWITCH\n"
         "\n"
-        "    Ctrl+s\n"
+        "    Ctrl+m\n"
         "        click on MENU\n"
         "\n"
         "    Ctrl+'+'\n"