Make Example comparable against names and sources

This will be needed for filtering examples.

src/spectator/example.cr

@@ -59,5 +59,21 @@ module Spectator
     def to_json(json : ::JSON::Builder)
       json.string(to_s)
     end
+
+    # Checks if this example matches some criteria.
+    # This is used to filter examples.
+    def ===(other)
+      other === to_s
+    end
+
+    # Checks if this example is at the specified source.
+    def ===(other : Source)
+      source == other
+    end
+
+    # Checks if this example is at the specified line number.
+    def ===(other : Int32)
+      source.line === other
+    end
   end
 end