* Move initial batch of shaders and presets to smoothing subdirectory
* Rename smoothing to edge enhancement
* Move cubic and windowed into interpolation
* Fix some presets
* Fix rest of presets
* Rename edge-enhancement to edge-smoothing
* Move pixel art scalers into separate directory separate from 'interpolation'
* Flatten interpolation/cubic into interpolation/
* Simplify pixel AA; Dependents to be refactored
* Finish refactoring pixel_aa itself; Dependent presets TBD
* Update average and border fill
* Tune default blur strengths in blur fill
* Clean up includes
* Minor corrections