Rename Spline to SimpleSpline

We're going to use Spline for the general case, so free up that name.
It's likely SimpleSpline will go away as it will be fully subsumed by
Spline, but it's also possible it will remain useful in some cases.

examples/rand.rs

@@ -7,7 +7,7 @@ use rand::distributions::{Distribution, Uniform};
 
 use kurbo::Point;
 
-use spline::Spline;
+use spline::SimpleSpline;
 
 fn main() {
     let mut rng = rand::thread_rng();
@@ -19,7 +19,7 @@ fn main() {
             Point::new(x, y)
         })
         .collect::<Vec<_>>();
-    let mut spline = Spline::new(pts.clone());
+    let mut spline = SimpleSpline::new(pts.clone());
     for iter_ix in 0..10 {
         let abs_err = spline.iterate(iter_ix);
         eprintln!("err: {}", abs_err);

src/lib.rs

@@ -11,8 +11,8 @@
 //! [research spline]: https://github.com/raphlinus/spline-research
 
 mod hyperbezier;
-mod spline;
+mod simple_spline;
 mod util;
 
 pub use hyperbezier::{HyperBezier, ThetaParams};
-pub use spline::Spline;
+pub use simple_spline::SimpleSpline;

src/spline.rs → src/simple_spline.rs

@@ -7,7 +7,7 @@ use kurbo::{Affine, BezPath, Point, Vec2};
 use crate::hyperbezier::{HyperBezier, HyperBezierResult, ThetaParams};
 use crate::util;
 
-pub struct Spline {
+pub struct SimpleSpline {
     pts: Vec<Point>,
     ths: Vec<f64>,
 }
@@ -18,10 +18,10 @@ struct Seg {
     d: Vec2,
 }
 
-impl Spline {
-    pub fn new(pts: Vec<Point>) -> Spline {
+impl SimpleSpline {
+    pub fn new(pts: Vec<Point>) -> SimpleSpline {
         let ths = Self::initial_ths(&pts);
-        Spline { pts, ths }
+        SimpleSpline { pts, ths }
     }
 
     fn initial_ths(pts: &[Point]) -> Vec<f64> {
@@ -150,7 +150,7 @@ impl Spline {
 
 fn bias_for_theta(th: f64) -> f64 {
     // Tangent angles up to this limit will be Euler spirals.
-    const EULER_LIMIT: f64 = 0.4 * PI;
+    const EULER_LIMIT: f64 = 0.3 * PI;
     let th = th.abs();
     if th < EULER_LIMIT {
         1.0