added slime overlay, colors chunks green if slimes can spawn

overviewer_core/src/overviewer.h

@@ -26,7 +26,7 @@
 
 // increment this value if you've made a change to the c extesion
 // and want to force users to rebuild
-#define OVERVIEWER_EXTENSION_VERSION 35
+#define OVERVIEWER_EXTENSION_VERSION 36
 
 /* Python PIL, and numpy headers */
 #include <Python.h>
@@ -88,6 +88,7 @@ typedef struct {
 } ChunkData;
 typedef struct {
     /* the regionset object, and chunk coords */
+    PyObject *world;
     PyObject *regionset;
     int chunkx, chunky, chunkz;