v0.5.1 - Resolution-related fixes

Turns out I'm somewhat of a irresponsible dev...

I didn't test all scenarios involving changing the screen resolution, so I ended up letting a few bugs slip into the previous release. These would only trigger if someone tried to change from windowed to fullscreen mode (and vice-versa) without also setting the screen resolution. I also forgot to evict the level select texture cache, so the level thumbnails would vanish after changing resolutions.

Since I was already changing things, I also pushed a minor QoL: now there's a shadow beneath the player!

Changelog

• Fix initializing the resolution in the options menu
• Evict level select's texture cache on resolution changed
• Add a simple pseudo-shadow to the player