code: public static TileGrid tileGridZoomIncrease(TileGrid tileGrid,
  			int zoomLevels) {
  		long minX = tileGridMinZoomIncrease(tileGrid.getMinX(), zoomLevels);
  		long maxX = tileGridMaxZoomIncrease(tileGrid.getMaxX(), zoomLevels);
  		long minY = tileGridMinZoomIncrease(tileGrid.getMinY(), zoomLevels);
  		long maxY = tileGridMaxZoomIncrease(tileGrid.getMaxY(), zoomLevels);
  		TileGrid newTileGrid = new TileGrid(minX, minY, maxX, maxY);
  		return newTileGrid;
  	}
docs: Get the tile grid starting from the tile grid and zooming in / increasing
  the number of levels
  
  @param tileGrid
  current tile grid
  @param zoomLevels
  number of zoom levels to increase by
  @return tile grid at new zoom level
  @since 2.0.1