fixes default option value (closes issue #26)

See #26 for context, but after these changes, we honor default options.

```
$ ./example.out
Commands
    mine == false
    move == false
    create == false
    remove == false
    set == false
    ship == false
    shoot == false
Arguments
    x == (null)
    y == (null)
Flags
    --drifting == false
    --help == false
    --moored == false
    --version == false
Options
    --speed == 10
```