Touch up Ray docs

src/cgmath/line.rs

@@ -22,7 +22,7 @@ use vector::{Vector, Vector2};
 use partial_ord::PartOrdFloat;
 use intersect::Intersect;
 
-/// A generic directed line segment
+/// A generic directed line segment from `origin` to `dest`.
 #[deriving(Clone, Eq)]
 pub struct Line<P>
 {

src/cgmath/ray.rs

@@ -16,7 +16,8 @@
 use point::{Point, Point2, Point3};
 use vector::{Vector, Vector2, Vector3};
 
-/// A generic ray
+/// A generic ray starting at `origin` and extending infinitely in
+/// `direction`.
 #[deriving(Clone, Eq)]
 pub struct Ray<P,V>
 {