code: func looksLikeError(i *ast.Ident) bool {
  	prefix := "err"
  	if i.IsExported() {
  		prefix = "Err"
  	}
  	return strings.HasPrefix(i.Name, prefix)
  }
docs: // looksLikeError returns true if the AST identifier starts
  // with 'err' or 'Err', or false otherwise.
  //
  // TODO: https://github.com/leighmcculloch/gochecknoglobals/issues/5