Remaining code from #25

[sritchie]

TODO:

• close the integrator when evolve shuts down, do it in a hook.
• note http://www.cs.cmu.edu/~kmcrane/Projects/Other/YarnCurve.pdf

(defn knitting [R r p q]
  (fn [theta]
    [(e/+ theta (e/* p (e/sin (e/* 2 theta))))
     (e/* q (e/cos theta))
     (e/* R (e/cos (e/* 2 theta)))]))