CmdList is hardcoded to 500 results.

Noticed this whilst looking thru the commands.go

```
json, err := jsonEncode(map[string]interface{}{¬
     "jql":        query,
     "startAt":    "0",
     "maxResults": "500",
     "fields":     fields,
})
```

I know we have projects with more than this open, so it would be great to expose this as an option.

(NB: i plan to submit a PR for this!)
