Added Block.getPistonMoveReaction, BlockPistonExtend and BlockPistonRetractEvent

By: Erik Broes <erikbroes@grum.nl>

paper-api/src/main/java/org/bukkit/event/Cancellable.java

@@ -1,6 +1,19 @@
 package org.bukkit.event;
 
 public interface Cancellable {
+    /**
+     * Gets the cancellation state of this event. A cancelled event will not
+     * be executed in the server, but will still pass to other plugins
+     *
+     * @return true if this event is cancelled
+     */
     public boolean isCancelled();
+
+    /**
+     * Sets the cancellation state of this event. A cancelled event will not
+     * be executed in the server, but will still pass to other plugins.
+     *
+     * @param cancel true if you wish to cancel this event
+     */
     public void setCancelled(boolean cancel);
 }