Thanks! I made it 2-3 years ago and IIRC it took me few months of weekend work; the things is that it was "easy" in the beginning, but for each combination of "feature" + "drawing type" things got a lot more complex, specially later on. e.g. when adding the option to shift the grid, or scale it, then I needed to change all of the drawing methods; or when I add a new drawing method, then it needs to work with all the other configs. So a lot of the code is basically dealings with these cases.
It also has a lot of logic trying to position things so that they look nice, specially around the axis arrows/numbers (since any overflow off the SVG would be cut off).
Unfortunately none. Once I finished the library I realized I was barking at the wrong tree, meaning this would probably be better for high-value high integration business (B2B) rather than to sell to small blogs that have maths in them at B2C prices. But then I also got a job and so while the library works just fine, I haven't put the energy into selling it.
It also has a lot of logic trying to position things so that they look nice, specially around the axis arrows/numbers (since any overflow off the SVG would be cut off).