Add spec helper for capturing stdout to a string

* Shout out to @avdi for his awesome RubyTapas!
* http://www.rubytapas.com/episodes/29-Redirecting-Output

Author: iamvery

spec/support/capture_stdout.rb

@@ -0,0 +1,11 @@
+require 'stringio'
+
+def capture_stdout
+  captured_output = StringIO.new
+  real_stdout = $stdout
+  $stdout = captured_output
+  yield
+ensure
+  $stdout = real_stdout
+  return captured_output.string
+end