Web version & some polishing

Hello! As the title says, WebGL version was added. But I still recommend downloading a standalone demo, because it's more responsive and stable. Also, a few changes were made to the game:

• Music is updated (each level has unique music).
• Tutorial improvements (I hope for the better).
• Sound volume customization option.
• More environment animations.
• Screen shake on 'bad events'.
• Slight changes in level design.
• Build size is reduced.