Indicate the default value even when allowedHelp is passed

[nex3]

Currently, if allowedHelp and default are both passed to ArgParser.addOption(), the help output doesn't indicate what the default value is. For example:

-r, --runner                   The runner used to print test results.

          [compact]            A single line, updated continuously.
          [expanded]           A separate line for each update.

Output like the following would be better:

-r, --runner                   The runner used to print test results.

      [compact (default)]      A single line, updated continuously.
      [expanded]               A separate line for each update.

[natebosch]

Closed with #100