Support paging through the output

zig/sdl/hello_sdl.zig

    c.SDL_StartTextInput();
    var quit = false;
    var skip: i32 = 0;
    while (!quit) {
        var event: c.SDL_Event = undefined;
        while (c.SDL_PollEvent(&event) != 0) {
                                msg[pos] = '_';
                            },
                            c.SDLK_RETURN => {
                                skip = 0;
                                gpa.free(result);
                                result = try runCommand(&msg, gpa);
                                var i: usize = 0;
                                msg[max_chars] = 0;
                                pos = 0;
                            },
                            c.SDLK_UP => {
                                if (skip > 0) {
                                    skip -= 1;
                                }
                            },
                            c.SDLK_PAGEUP => {
                                if (skip < 10) {
                                    skip = 0;
                                } else {
                                    skip -= 10;
                                }
                            },
                            c.SDLK_DOWN => {
                                skip += 1;
                            },
                            c.SDLK_PAGEDOWN => {
                                skip += 10;
                            },
                            else => {},
                        }
                    }
        var i: c_int = 1;
        var lines = std.mem.split(result, "\n");
        var line = lines.next();
        while (line != null) {
        {
            var skipped: i32 = 0;
            while (skipped < skip and line != null) : (skipped += 1) {
                line = lines.next();
            }
        }
        while (line != null and i * glyph_height < window_height) {
            const line_c = try gpa.dupeZ(u8, line.?);
            const result_text = c.TTF_RenderUTF8_Shaded(font, line_c, white, black);
            gpa.free(line_c);