Lennart Regebro <regebro@gmail.com>, Original Author

Justin Gruenberg implemented the Quadradic Bezier calculations and
provided suggestions and feedback about the d() function.

Michiel Schallig suggested calculating length by recursive straight-line
approximations, which enables you to choose between accuracy or speed.
Steve Schwarz added an error argument to make that choice an argument.

Thanks also to bug fixers Martin R, abcjjy, Daniel Stender and MTician.