SDL2 sample: Add key binding for toggling visual debugger

For the sake of completeness and consistency with the documentation.
Good catch -- I learn something new every day! :-) After a quick look over SDL_keycode.h and SDL_scancode.h .. I do not believe so. 

I did find SDL_SCANCODE_GRAVE:
```
    SDL_SCANCODE_GRAVE = 53, /**< Located in the top left corner (on both ANSI
                              *   and ISO keyboards). Produces GRAVE ACCENT and
                              *   TILDE in a US Windows layout and in US and UK
                              *   Mac layouts on ANSI keyboards, GRAVE ACCENT
                              *   and NOT SIGN in a UK Windows layout, SECTION
                              *   SIGN and PLUS-MINUS SIGN in US and UK Mac
                              *   layouts on ISO keyboards, SECTION SIGN and
                              *   DEGREE SIGN in a Swiss German layout (Mac:
                              *   only on ISO keyboards), CIRCUMFLEX ACCENT and
                              *   DEGREE SIGN in a German layout (Mac: only on
                              *   ISO keyboards), SUPERSCRIPT TWO and TILDE in a
                              *   French Windows layout, COMMERCIAL AT and
                              *   NUMBER SIGN in a French Mac layout on ISO
                              *   keyboards, and LESS-THAN SIGN and GREATER-THAN
                              *   SIGN in a Swiss German, German, or French Mac
                              *   layout on ANSI keyboards.
                              */
```

I'm ignorant of non-US keyboard layouts, but this does *appear* to me as a rough equivalent, aye? I swapped out checking for event.key.keysym.sym with event.key.keysym.scancode and it does work as intended. Is this safe / sane to use?

Cheers,
Jeffrey Carpenter
<i8degrees@gmail.com>

On 2014/10/ 31, at 9:17, David Wimsey <notifications@github.com> wrote:

> In Samples/basic/sdl2/src/main.cpp:
> 
> > @@ -138,8 +138,20 @@ int main(int argc, char **argv)
> >                      break;
> >  
> >                  case SDL_KEYDOWN:
> > +                {
> > +                    // Intercept SHIFT + ~ key stroke to toggle libRocket's 
> > +                    // visual debugger tool
> > +                    if( event.key.keysym.sym == SDLK_BACKQUOTE && 
> 
> Is there a scan code for Tilde in SDL? Tilde doesn't always match up with the backquote depending on keyboard layout/culture
> 
> —
> Reply to this email directly or view it on GitHub.
>