- Replace MedianBlendedImage with StitchedImage, a general implementation of a stitcher
- Don't use hilbert curve when regenerating cache image
- Cut workload rectangles to be always inside the cache image boundaries
- Rename stitch.go to main.go
- Add interface for overlays
- Change how overlays are handled and drawn
- Reduce error returns to simplify a lot of code
- Add several blend functions
- Remove offset field from image tile
