Record videos at any duration
Currently, it's possible to record only 4 seconds of gameplay. You hit F10 once, and it will automatically generate one `webm` file.
**[This is being handled here, at line 148](https://github.com/aduros/wasm4/blob/81324408bbae98719e13c9579c31d400be8fc229/runtimes/web/src/index.js#L148)**.

It would be cool if we could record longer videos, though. So I think video recording could be done like this:
1. Press F10 once.
2. Gameplay is now being recorded. We could set some sort of indicator on top of the screen, so you don't forget to stop the recording later.
3. Press F10 again, and it will immediately stop the recording and generate one `webm` file for you.
4. If you forget to press F10 again, the recording will stop after a certain time limit (*30 seconds?*).