Bevy 0.15 initial support

[Leinnan]

What it does:

• adds support for newest bevy
• updates some of the samples

What it does not:

• updates and confirms that all samples are working
• updates naming of code to match newest bevy naming

[SergioRibera]

Hello, thank you very much for the contribution, it is really nice, I left some comments with suggestions for changes if you like to discuss it, I am totally open to it 😃

[SergioRibera]

Thank you very much for your contribution 🙌🏻

[Leinnan]

No problem! It still requires updating rest of the samples and I would consider updating naming a bit and take more advantage of the introduced requiredComponents feature, but it is a good start for that!

Thanks for creating this useful crate!