Add a silent formatter

src/spectator/formatters/silent_formatter.cr

@@ -0,0 +1,27 @@
+module Spectator::Formatters
+  # Formatter that outputs nothing.
+  # Useful for testing and larger automated processes.
+  class SilentFormatter < Formatter
+    # Called when a test suite is starting to execute.
+    def start_suite(suite : TestSuite)
+      # ... crickets ...
+    end
+
+    # Called when a test suite finishes.
+    # The results from the entire suite are provided.
+    def end_suite(report : Report)
+      # ... crickets ...
+    end
+
+    # Called before a test starts.
+    def start_example(example : Example)
+      # ... crickets ...
+    end
+
+    # Called when a test finishes.
+    # The result of the test is provided.
+    def end_example(result : Result)
+      # ... crickets ...
+    end
+  end
+end