Change dziOverlap to 2

With 0, OpenSeadragon has problems drawing the images correctly.
And with 1, we introduce rounding errors when creating the smaller zoom levels.

bin/stitch/dzi.go

@@ -19,7 +19,7 @@ import (
 
 const (
 	dziTileSize = 512 // The (maximum) width and height of a tile in pixels, not including the overlap.
-	dziOverlap  = 0   // The amount of additional pixels on every side of every tile. The real (max) width/height of an image is `2*overlap + tileSize`.
+	dziOverlap  = 2   // The amount of additional pixels on every side of every tile. The real (max) width/height of an image is `2*overlap + tileSize`.
 )
 
 type DZI struct {