add plugin infrastructure

src/event.rs

@@ -0,0 +1,25 @@
+use std::fmt::Debug;
+
+use std::any::Any;
+
+pub struct AbstractEvent {
+    inner: Box<Any>,
+}
+
+impl AbstractEvent {
+    pub fn new<E: Event>(event: E) -> AbstractEvent {
+        AbstractEvent {
+            inner: Box::new(event),
+        }
+    }
+
+    pub fn downcast<E: Event + 'static>(&self) -> Option<&E> {
+        self.inner.downcast_ref::<E>()
+    }
+
+    pub fn is<E: Event + 'static>(&self) -> bool {
+        self.inner.is::<E>()
+    }
+}
+
+pub trait Event: Any + Debug {}