Full screen support and game menu

Full-screen support has been added as well as a simple menu with some options:

• Full-screen check: Toggle fullscreen mode.
• Objective marker check: if activated an arrow will point to the current objective.
• Volume bar: Now you can lower or raise the volume at your will.
• Close menu button
• Exit game button

Some minor corrections have been made to the game as well, just some polish.

* Note that with the web version, the full-screen mode is handled by the bottom right button that itch.io offers and the ESC key to get back to windowed mode.