Support listing all issues, instead of just open/closed

[lawrencejones]

I use ghi to append issues into my git commit messages. It's really useful to see all issues, rather than just the issues I've got open, and I don't want to have to wait for two separate requests to complete before I view all my issues.

At the moment ghi only supports open/closed states. This seems pretty restrictive seeing as githubs api actually allows for an all state.

[AlexChesters]

Hi @lawrencejones,

This is a great idea and definitely something we'd like to see.

~~I see you've made a commit on this, if it's in a good state would you mind opening a PR?~~

I've just checked out your branch and when I run git list -a or git list --all it lists all issues I have read access too, rather than all issues for the current repo

[peterwwillis]

Hello, I have created a similar PR here with test results: https://github.com/stephencelis/ghi/pull/374

I believe this is only showing issues created for this repo by default, not global issues.