Customisable Klein bottle (OpenSCAD)

I saw this (quite old) challenge online:
https://www.makerbot.com/media-center/2011/10/11/openscad-challenge-klein-bottle

I could not resist making my own! I'm perfectionist, I made it as perfect as I could.

I made it using bezier curves because that was a lot easier than trying to model the shape by removing "donnut" shapes around it (I could not see a neat solution to do this). Since there is no bezier functionality in OpenSCAD, I had to create my own, from an existing library found on