Add 'all' state and options

[peterwwillis]

Here is a small change to support viewing open and closed issues.

Tested in a separate repo, test results:

psypete@windows:~/git/devopsyoga-content-local/edit-ghi (gh-pages)$ ~/git/ghi/ghi list      
# peterwwillis/devopsyoga-content open issues
  1: Test issue: open  test 
psypete@windows:~/git/devopsyoga-content-local/edit-ghi (gh-pages)$ ~/git/ghi/ghi list -s closed
# peterwwillis/devopsyoga-content closed issues
  2: Test issue: closed  test  1
psypete@windows:~/git/devopsyoga-content-local/edit-ghi (gh-pages)$ ~/git/ghi/ghi list --all
# peterwwillis/devopsyoga-content all issues
  2: Test issue: closed  test  1
  1: Test issue: open  test 
psypete@windows:~/git/devopsyoga-content-local/edit-ghi (gh-pages)$ ~/git/ghi/ghi list -s all
# peterwwillis/devopsyoga-content all issues
  2: Test issue: closed  test  1
  1: Test issue: open  test