Emscripten input callbacks

[HDAKFD]

Could there be an option to disable these emscripten input callbacks from getting registered. They're causing a lot of issues when trying to mess with html elements.

emscripten_set_keydown_callback,
emscripten_set_keyup_callback,
emscripten_set_keypress_callback

These are the main part of my issue since they just make emscripten to call event.preventDefault() for every html element with input.

[slouken]

We can definitely add a hint for this.

[icculus]

You should be able to use an existing hint. Just call...

SDL_SetHint(SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT, "some-element-id-that-doesnt-exist-on-the-page");

...any time before SDL_CreateWindow, and it won't register an input callback at all.

[icculus]

Okay, I've updated it so setting SDL_HINT_EMSCRIPTEN_KEYBOARD_ELEMENT to "" will stop SDL from setting those input callbacks at all, so no weird hacks with bogus element names.

[slouken]

I switched it to "#none". We use "" everywhere else as synonymous with NULL.