Upgrade to Bevy 0.14

[rparrett]

Upgrades to Bevy 0.14
Fixes #4

• Update bevy dep
• Update image dep to match bevy's
• One easy migration for bevy's changes to Color.

This also fixes a panic in terrain.rs which was unrelated to the Bevy upgrade.

I tested this with the examples from README.md. Those examples work as-is with Bevy 0.14 and don't require any changes. (Except for the previously mentioned panic related to terrain)

I would love to add these examples as cargo examples (I did this while testing), but I've omitted that here to keep things simple. I can follow up with that later if you're agreeable.

[manankarnik]

Sure @rparrett, feel free to raise a PR if you have worked on it.