Added two test cases from sublee/trueskill.

src/gaussian.rs

@@ -9,7 +9,7 @@ pub struct Gaussian {
 
 impl fmt::Debug for Gaussian {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "N(mu={:.03}, sigma={:.03})", self.mu(), self.sigma())
+        write!(f, "N(mu={:.03}, sigma={:.03}, pi={:.03}, tau={:.03})", self.mu(), self.sigma(), self.pi(), self.tau())
     }
 }