Added Debug, Display, and Default to Vectors and Quaternions.

This also adds an example for Vectors and Quaternions.

src/quaternion.rs

@@ -3,6 +3,7 @@
 //!
 //! [1]: https://en.wikipedia.org/wiki/Quaternion
 //! [2]: https://en.wikipedia.org/wiki/Dual_quaternion
+use std::fmt::{Error, Formatter, Debug, Display};
 use std::ops::{Add, Sub, Mul, Div, Neg};
 
 use ::zero::Zero;
@@ -275,6 +276,34 @@ impl<T> Quaternion<T> where T: Real
    // TODO: Add binary operations for editing self.
 }
 
+// Implement the Debug trait for the Quaternion.
+impl<T> Debug for Quaternion<T> where T: Real
+{
+   fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error>
+   {
+      write!(formatter, "[{:?}, {:?}]", self.scalar, self.vector)
+   }
+}
+
+// Implement the Display trait for the Quaternion.
+impl<T> Display for Quaternion<T> where T: Real
+{
+   fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error>
+   {
+      write!(formatter, "[{}, {}]", self.scalar, self.vector)
+   }
+}
+
+// Implement a default value for Quaternions which
+// returns the identity quaternion.
+impl<T> Default for Quaternion<T> where T: Real
+{
+   fn default() -> Quaternion<T>
+   {
+      Quaternion::identity()
+   }
+}
+
 // Implement the Zero and One traits for the Quaternion.
 impl<T> Zero for Quaternion<T> where T: Real
 {