Complete Rust API and migration documentation (#102)

crates/libremetaverse/examples/cancellation.rs

@@ -0,0 +1,14 @@
+use libremetaverse_types::compat::CancellationTokenSource;
+
+#[tokio::main(flavor = "current_thread")]
+async fn main() -> Result<(), libremetaverse::Error> {
+    let source = CancellationTokenSource::new();
+    let token = source.token();
+    source.cancel();
+    token.cancelled().await;
+    assert!(matches!(
+        token.throw_if_cancellation_requested(),
+        Err(libremetaverse::Error::Cancelled)
+    ));
+    Ok(())
+}