Add some new blocks for Minecraft 1.9

* Purpur blocks, pillars, stairs, and slabs
* End brick

overviewer_core/src/iterate.c

@@ -263,6 +263,7 @@ is_stairs(int block) {
         case 163: /* acacia wood stairs */
         case 164: /* dark wood stairs */
         case 180: /* red sandstone stairs */
+        case 203: /* purpur stairs */
             return 1;
     }
     return 0;