Fallback to flat when no oxr runtime is found (#51)

* basics done? now to the fun part: changing the ENTIRE lib to work with xr and non xr

* updated stuff and renamed file

* actually add the renamed file into git lol :3

* made lib fallback to flat when no runtime is found but can't compile with default settings under those circumstances

examples/demo/Cargo.toml

@@ -17,4 +17,5 @@ color-eyre = "0.6.2"
 
 [target.'cfg(not(target_os="android"))'.dependencies.bevy_oxr]
 path = "../../"
+# May need to be more specific. needs to be false at least on linux without an active runtime to run in flat
 default-features = true