Window icon settings added

[joffreybesos]

I added window_icon and taskbar_icon to the window builder.
This will accept an optional path to a file to use.
It should work with jpeg, png and ico files.

I have only tested this on windows.

I also updated the window_config example to include these two settings, and a rust.ico asset file.
There's an ugly load_icon function added in notan_winit window.rs but wasn't sure of where else to place it.

e.g.

    let window_config = WindowConfig::new()
        .title("Window Config Demo")
        .size(1026, 600) // window's size
        .vsync(true) // enable vsync
        .resizable(true) // window can be resized
        .min_size(600, 400) // Set a minimum window size
        .window_icon(Some(PathBuf::from("./examples/assets/rust.ico")))
        .taskbar_icon(Some(PathBuf::from("./examples/assets/rust.ico")));

[Nazariglez]

This looks great! I just fixed the compilation for other platforms. Once the CI is done, I'll merge it.

Thank you so much!