Add support for ChunkSnapshot API (CB860), maintain legacy support too

src/main/java/org/dynmap/utils/LegacyChunkSnapshot.java

@@ -0,0 +1,46 @@
+package org.dynmap.utils;
+
+/**
+ * Represents a static, thread-safe snapshot of chunk of blocks
+ * Purpose is to allow clean, efficient copy of a chunk data to be made, and then handed off for processing in another thread (e.g. map rendering)
+ */
+public interface LegacyChunkSnapshot {
+    /**
+     * Get block type for block at corresponding coordinate in the chunk
+     * 
+     * @param x 0-15
+     * @param y 0-127
+     * @param z 0-15
+     * @return 0-255
+     */
+    public int getBlockTypeId(int x, int y, int z);
+    /**
+     * Get block data for block at corresponding coordinate in the chunk
+     * 
+     * @param x 0-15
+     * @param y 0-127
+     * @param z 0-15
+     * @return 0-15
+     */
+    public int getBlockData(int x, int y, int z);
+    /**
+     * Get sky light level for block at corresponding coordinate in the chunk
+     * 
+     * @param x 0-15
+     * @param y 0-127
+     * @param z 0-15
+     * @return 0-15
+     */
+    public int getBlockSkyLight(int x, int y, int z);
+    /**
+     * Get light level emitted by block at corresponding coordinate in the chunk
+     * 
+     * @param x 0-15
+     * @param y 0-127
+     * @param z 0-15
+     * @return 0-15
+     */
+    public int getBlockEmittedLight(int x, int y, int z);
+
+    public int getHighestBlockYAt(int x, int z);
+}