Add to_s methods for result types

src/spectator/errored_result.cr

@@ -17,5 +17,10 @@ module Spectator
       value = yield self
       interface.error(value)
     end
+
+    # One-word descriptor of the result.
+    def to_s(io)
+      io << "error"
+    end
   end
 end

src/spectator/failed_result.cr

@@ -27,5 +27,10 @@ module Spectator
       value = yield self
       interface.failure(value)
     end
+
+    # One-word descriptor of the result.
+    def to_s(io)
+      io << "fail"
+    end
   end
 end

src/spectator/pending_result.cr

@@ -16,5 +16,10 @@ module Spectator
       value = yield self
       interface.pending(value)
     end
+
+    # One-word descriptor of the result.
+    def to_s(io)
+      io << "pending"
+    end
   end
 end

src/spectator/successful_result.cr

@@ -14,5 +14,10 @@ module Spectator
       value = yield self
       interface.success(value)
     end
+
+    # One-word descriptor of the result.
+    def to_s(io)
+      io << "success"
+    end
   end
 end