add section: references and further reading

[mikolalysenko]

None of the content of this article refers to any prior work, or gives the reader any hint of where to look for further information.

[Pomax]

that's because it doesn't build on any prior work beyond "generic information you get when you look up bezier curves the normal way". The original article has a section on fat line clipping, which definitely builds on prior work and links out to that, but it's not the most useful algorithm so I'm probably not adding it back in. Some of the sections link out to relevant material in the text, but a separate section for further reading might not be a bad idea. Changed the issue title to reflect this.