Update bracket-bevy to support bevy 0.15

[alkumis]

For anyone who wants to use bracket-bevy from backet-lib to use the roguelike tutorial with the latest version of bevy.

I made minimal updates to get the bracket-bevy crate to run on bevy 0.15. All the bracket-bevy examples run now.

Also exposed bracket-bevy as 'bevy' on the bracket-lib crate for ease of use.

Edit: forgot to mention I updated bracket color and bracket geometry to point to bevy 0.15 as well with minimal changes