example experiment (unfinished)
musings on style parameterisation
started refactoring, but ran into some problems

thinking required
put line style in Curve instead of Curves
-hide-package monads-tf also in style-refactor branch
parameterise line style by pixel position
fixed rendering bug with variable width curves

closest point on the curve needs to take the line width (and blur) at the
candidate points into account
added freezeImageStyle
Fixed silly bug introduced in toSegments
improved implementation of differentiate
added sampleImage (mostly for testing)
example with differentiate and freezeImageStyle