feat(API): Use mio::Token based polling

Avoid polling every single IO source to collect events,
poll those specific IO sources mio tells us about.

util/src/option.rs

@@ -0,0 +1,7 @@
+pub trait SomeExt: Sized {
+    fn some(self) -> Option<Self> {
+        Some(self)
+    }
+}
+
+impl<T> SomeExt for T {}