Add Rerecast and remove bevy_fix_gltf_coordinate_system (#560)

Author: janhohenheim

Assets/AI/bevy_rerecast.toml

@@ -0,0 +1,5 @@
+name = "bevy_rerecast"
+description = "Rust port of Recast, the industry-standard navigation mesh generator."
+link = "https://github.com/janhohenheim/rerecast"
+crate = "bevy_rerecast"
+image = "rerecast.jpg"