add matrix exponentiation as op overload example

Author: TimToady

features.json

@@ -699,7 +699,8 @@
         "item"    : "Overloading operators",
         "status"  : "rm+ rn+ n+",
         "code"    : [ "http://perl6advent.wordpress.com/2009/12/22/day-22-operator-overloading/",
-                      "http://rosettacode.org/wiki/Quaternion_type#Perl_6" ],
+                      "http://rosettacode.org/wiki/Quaternion_type#Perl_6",
+		      "http://rosettacode.org/wiki/Matrix-exponentiation_operator#Perl_6" ],
         "spec"    : [ ]
       }, {
         "item"    : "Defining new operators",