Figure out how to best split an image into tiles

[oubiwann]

This will not only involve image processing, but maybe also involve creating a RoaringBitmap for use as a tile.

Possibly useful as reference or inspiration:

• https://github.com/rikonor/go-imgsplit/blob/master/split.go
• https://github.com/rikonor/go-imgsplit/blob/master/quadtree.go
• https://github.com/rikonor/go-imgsplit/blob/master/utils.go
• https://github.com/rikonor/go-imgutil/blob/master/iterate.go
• https://github.com/RoaringBitmap/roaring#example
• https://godoc.org/github.com/RoaringBitmap/roaring
• https://github.com/asim/quadtree
• https://godoc.org/github.com/asim/quadtree
• https://github.com/google/hilbert#how-to-use