Added various new 1.9 entities, blocks and items

By: Nathan Adams <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/entity/MushroomCow.java

@@ -0,0 +1,8 @@
+package org.bukkit.entity;
+
+/**
+ * Represents a mushroom {@link Cow}
+ */
+public interface MushroomCow extends Cow {
+    
+}