message: das.Cli.Option: Add constructor without short option.
diff: @@ -160,7 +160,7 @@ namespace elle
  struct Option
  {
  - Option(char short_name = 0,
  + Option(char short_name,
  std::string help = "",
  bool positional = false)
  : short_name(short_name)
  @@ -168,6 +168,13 @@ namespace elle
  , positional(positional)
  {}
  + Option(std::string help = "",
  + bool positional = false)
  + : short_name(0)
  + , help(std::move(help))
  + , positional(positional)
  + {}
  +
  char short_name;
  std::string help;
  bool positional;
  