Implement Default for Quaternion and UnitQuaternion.

src/geometry/quaternion.rs

@@ -30,6 +30,14 @@ pub struct Quaternion<N: RealField> {
     pub coords: Vector4<N>,
 }
 
+impl<N: RealField> Default for Quaternion<N> {
+    fn default() -> Self {
+        Quaternion {
+            coords: Vector4::zeros()
+        }
+    }
+}
+
 #[cfg(feature = "abomonation-serialize")]
 impl<N: RealField> Abomonation for Quaternion<N>
 where Vector4<N>: Abomonation
@@ -1422,6 +1430,12 @@ impl<N: RealField> UnitQuaternion<N> {
     }
 }
 
+impl<N: RealField> Default for UnitQuaternion<N> {
+    fn default() -> Self {
+        Self::identity()
+    }
+}
+
 impl<N: RealField + fmt::Display> fmt::Display for UnitQuaternion<N> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if let Some(axis) = self.axis() {