Combine Racers 0.4.0

This is just a small release with some minor improvements and engine upgrades.

• Upgraded to Bevy 0.12 (previous itch release used Bevy 0.9)
• Added shadow options, and enabled high quality filtering for shadows by default.
• Added a tiling/scrolling background.
• Added a simple boost gauge.
• Added a title to the window.
• Fixed the console opening when running the Windows build.