Improve EventBus Javadoc, make EventBusException final

As suggested by @delvh.

@@ -74,0 +75,4 @@
+	private final Map<Class<?>, TreeSet<EventHandler>> bindings = new ConcurrentHashMap<>();
+
+	/**
+	 * Registered listeners.

@@ -74,0 +82,4 @@
+	private final Set<Object> registeredListeners = ConcurrentHashMap.newKeySet();
+
+	/**
+	 * Thread-local dispatch state.

@@ -4,3 +4,1 @@
- * This runtime exception is thrown when an event bus error occurs. This can
- * either occur while registering event listeners with invalid handlers, or when
- * an event handler throws an exception.
+ * This unchecked exception is specific to the event bus and can be thrown under the following

@@ -7,0 +4,4 @@
+ * This unchecked exception is specific to the event bus and can be thrown under the following
+ * circumstances:
+ * <ul>
+ * <li>An event handler throws an exception (which is stores as the cause)</li>