Allow shortcuts to be configurable

[Valmar33]

Allow shortcuts to be configurable through a config file or something, as I have discovered to my dismay that my new keyboard doesn't have a Meta key. :(

[Sethox]

I tried to pull request (provide code) to this project. But I am stuck (basically my knowledge of C++ and C is limited.
I narrowed it down to file from row 114 to understand the scope of what's happening (pun not intended).
Further down on to the switch case (still same bracket, row 146):

switch ( key ) {
	case KEY_F:
		g_bFullscreen = !g_bFullscreen;
		SDL_SetWindowFullscreen( g_SDLWindow, g_bFullscreen ? SDL_WINDOW_FULLSCREEN_DESKTOP : 0 );
		break;
	case KEY_N:
		g_bFilterGameWindow = !g_bFilterGameWindow;
		break;
	case KEY_U:
		g_fsrUpscale = !g_fsrUpscale;
		break;
	case KEY_I:
		g_fsrSharpness = std::min(20, g_fsrSharpness + 1);
		break;
	case KEY_O:
		g_fsrSharpness = std::max(0, g_fsrSharpness - 1);
		break;
	case KEY_S:
		take_screenshot();
		break;
	default:
		handled = false;
}

I can "see" certain shortcuts being defined. Basically, if I start to look/track code from here (follow it up to the defined super key). I will continue later on later, leaving it here for now as a note to pick it up later on (unless someone else continues).

[thingsiplay]

I hope this can be configured soon, because it interferes with my window management shortcuts which I do not want to change. They follow a specific logic and makes sense in relation to all other shortcuts I have.