added MaterialData classes and associated Enums for COAL, CROPS, LOG, LEAVES, STEP, and DOUBLE_STEP

By: sunkid <sunkid@iminurnetz.com>

paper-api/src/main/java/org/bukkit/material/Leaves.java

@@ -0,0 +1,44 @@
+package org.bukkit.material;
+
+import org.bukkit.Material;
+import org.bukkit.TreeSpecies;
+
+/**
+ * Represents the different types of leaves.
+ * @author sunkid
+ */
+public class Leaves extends MaterialData {
+    public Leaves(final int type) {
+        super(type);
+    }
+
+    public Leaves(final Material type) {
+        super(type);
+    }
+
+    public Leaves(final int type, final byte data) {
+        super(type, data);
+    }
+
+    public Leaves(final Material type, final byte data) {
+        super(type, data);
+    }
+
+    /**
+     * Gets the current species of this leave
+     *
+     * @return TreeSpecies of this leave
+     */
+    public TreeSpecies getSpecies() {
+        return TreeSpecies.getByData(getData());
+    }
+
+    /**
+     * Sets the species of this leave
+     *
+     * @param species New species of this leave
+     */
+    public void setSpecies(TreeSpecies species) {
+        setData(species.getData());
+    }
+}