Add types to represent coordinates

These will be used to improve the usability of `Point` and `Vector`.

src/math/coordinates.rs

@@ -0,0 +1,24 @@
+#![allow(unused)]
+
+use super::Scalar;
+
+/// 1-dimensional curve coordinates
+#[repr(C)]
+pub struct T {
+    pub t: Scalar,
+}
+
+/// 2-dimensional surface coordinates
+#[repr(C)]
+pub struct Uv {
+    pub u: Scalar,
+    pub v: Scalar,
+}
+
+/// 3-dimensional model coordinates
+#[repr(C)]
+pub struct Xyz {
+    pub x: Scalar,
+    pub y: Scalar,
+    pub z: Scalar,
+}

src/math/mod.rs

@@ -1,4 +1,5 @@
 pub mod aabb;
+pub mod coordinates;
 pub mod point;
 pub mod scalar;
 pub mod segment;