fixed errors removing tiles with coordinate and calculating position for non-isometric tiles

fixed errors removing tiles with coordinate and calculating position for non-isometric tiles
Hey, finally got around to looking at this.  Curious what the reason for changing from the tileset size to the layer size fixes.  I recently changed this to fix another issue by using the tileset tile size.  (https://github.com/slycrel/JSTileMap/issues/8)