Update examples

- Updates deps
- Some README updates considering the Winit backend based on
  android-activity has been merged upstream
- runs cargo fmt over examples
- Top-level Cargo.toml simply excludes "examples" instead of
  listing each sub-directory separately

examples/na-mainloop/src/lib.rs

@@ -1,4 +1,4 @@
-use android_activity::{AndroidApp, MainEvent, PollEvent, InputStatus};
+use android_activity::{AndroidApp, InputStatus, MainEvent, PollEvent};
 use log::info;
 
 #[no_mangle]