init. add linear interpolation

- just horizontal for now
- noisy (i.e. very dark) edges yield bad results
- needs preprocessing or different approach
add layered flood fill

- looks not bad
- however, yields (of course) constant areas
- linear interpolation would be better
add layered flood fill result image
add vertical linear interpolation

- try averaging and selecting brighter value
- still problem with border artifacts
add edge sharpening

- seems promising
extend to 8-way-neighbourhoods. add threshold

- even better
curiously apply sharpening repeatedly
make linear avg/max optional. add median filter. testing

- sophisticated result with median filter of size 5
- need to reimplement median filter
- need to evaluate runtime. all in all might be too slow
refactor: move sharpening to common, add comments, add floodfill forward declarations
add O(1) median filter paper
push to github. add license