Added Boat interface.

By: sk89q <the.sk89q@gmail.com>

paper-api/src/main/java/org/bukkit/Boat.java

@@ -0,0 +1,9 @@
+package org.bukkit;
+
+/**
+ * Represents a boat entity.
+ * 
+ * @author sk89q
+ */
+public interface Boat extends Vehicle {
+}