Rename `Stretch` to `Bow`

I wanted to name it `String` (as in bowstring), but it's taken in Rust,
and `Bowstring` is longer than just `Bow`, and the thing in question is
very much bow-shaped, so I went with `Bow`.

src/bow.rs

@@ -3,7 +3,7 @@ use petgraph::stable_graph::StableDiGraph;
 use crate::primitive::{Dot, Seg, Bend};
 use crate::graph::{TaggedIndex, DotIndex, SegIndex, BendIndex, TaggedWeight, Label, Path};
 
-pub struct Stretch<'a> {
+pub struct Bow<'a> {
     seg1_dot1: DotIndex,
     seg1: SegIndex,
     seg1_dot2: DotIndex,
@@ -14,7 +14,7 @@ pub struct Stretch<'a> {
     graph: &'a StableDiGraph<TaggedWeight, Label, usize>,
 }
 
-impl<'a> Stretch<'a> {
+impl<'a> Bow<'a> {
     pub fn new(index: BendIndex, graph: &'a StableDiGraph<TaggedWeight, Label, usize>) -> Self {
         let bend = index;
 
@@ -39,7 +39,7 @@ impl<'a> Stretch<'a> {
     }
 }
 
-impl<'a> Path for Stretch<'a> {
+impl<'a> Path for Bow<'a> {
     fn interior(&self) -> Vec<TaggedIndex> {
         vec![
             TaggedIndex::Seg(self.seg1),

src/layout.rs

@@ -155,9 +155,9 @@ impl Layout {
 
         let mut cur_bend = bend;
         while let Some(outer) = self.mesh.primitive(cur_bend).outer() {
-            let stretch = self.mesh.stretch(outer);
+            let bow = self.mesh.bow(outer);
-            endss.push(stretch.ends());
+            endss.push(bow.ends());
-            interiors.push(stretch.interior());
+            interiors.push(bow.interior());
             cur_bend = outer;
         }
 

src/main.rs

@@ -4,7 +4,7 @@ extern crate sdl2;
 mod layout;
 mod rules;
 mod mesh;
-mod stretch;
+mod bow;
 mod primitive;
 mod shape;
 mod math;

src/mesh.rs

@@ -8,7 +8,7 @@ use rstar::primitives::GeomWithData;
 use crate::primitive::Primitive;
 use crate::shape::Shape;
 use crate::graph::{Tag, TaggedIndex, DotIndex, SegIndex, BendIndex, Index, TaggedWeight, DotWeight, SegWeight, BendWeight, Label, Path};
-use crate::stretch::Stretch;
+use crate::bow::Bow;
 
 pub type RTreeWrapper = GeomWithData<Shape, TaggedIndex>;
 
@@ -123,8 +123,8 @@ impl Mesh {
         Primitive::new(index, &self.graph)
     }
 
-    pub fn stretch(&self, bend: BendIndex) -> Stretch {
+    pub fn bow(&self, bend: BendIndex) -> Bow {
-        Stretch::new(bend, &self.graph)
+        Bow::new(bend, &self.graph)
     }
 
     fn insert_into_rtree(&mut self, index: TaggedIndex) {