Add Event#cancel() convenience method (#94)

Author: PaintNinja

src/main/java/net/minecraftforge/eventbus/api/Event.java

@@ -73,8 +73,7 @@ public boolean isCanceled() {
      * @param cancel The new canceled value
      */
     public void setCanceled(boolean cancel) {
-        if (!isCancelable())
-        {
+        if (!isCancelable()) {
             throw new UnsupportedOperationException(
                 "Attempted to call Event#setCanceled() on a non-cancelable event of type: "
                 + this.getClass().getCanonicalName()
@@ -87,6 +86,13 @@ public void setCanceled(boolean cancel) {
         isCanceled = cancel;
     }
 
+    /**
+     * Equivalent to calling {@link #setCanceled(boolean)} with {@code true}.
+     */
+    public void cancel() {
+        setCanceled(true);
+    }
+
     /**
      * Determines if this event expects a significant result value.
      *