HTML5 Export

I've added an HTML5 version of the game.

Originally, I was using the mono version of Godot, but I only programmed in GDScript in order to publish HTML5. However, it turns out that you can't publish HTML with the mono version, even if you never use C#.

I decided to go back and try exporting the project with the vanilla 3.0.4 version of godot, and lucky me, everything works fine!

Next release, I'll make sure to use the non-mono version of godot to export, in order to remove the unnecessary mono requirement.