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

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

@@ -0,0 +1,40 @@
+package org.dynmap.utils;
+import org.bukkit.World;
+import org.dynmap.DynmapChunk;
+
+public interface MapChunkCache {
+    /**
+     * Load chunks into cache
+     * @param w - world
+     * @param chunks - chunks to be loaded
+     */
+    void loadChunks(World w, DynmapChunk[] chunks);
+    /**
+     * Unload chunks
+     */
+    void unloadChunks();
+    /**
+     * Get block ID at coordinates
+     */
+    int getBlockTypeID(int x, int y, int z);
+    /**
+     * Get block data at coordiates
+     */
+    byte getBlockData(int x, int y, int z);
+    /**
+     *  Get highest block Y
+     */
+    int getHighestBlockYAt(int x, int z);
+    /**
+     *  Get sky light level
+     */
+    int getBlockSkyLight(int x, int y, int z);
+    /**
+     * Get emitted light level
+     */
+    int getBlockEmittedLight(int x, int y, int z);
+    /**
+     * Get cache iterator
+     */
+    public MapIterator getIterator(int x, int y, int z);
+}