Allow a writer to be set that represents Stdout so that redirection of App output may occur.
Rename Stdout -> Writer
Merge remote-tracking branch 'origin/master' into allow-writer-to-be-set

Conflicts:
	app.go
	help.go
Prefer fmt.Fprint* functions over io.WriteString

Less composition needed.
Renaming fakeWriter to mockWriter for consistency
Merge pull request #154 from codegangsta/allow-writer-to-be-set

Allow writer to be set