Feature request: Add --comment to multi-gitter close

[jtgrohn]

The feature request
Add --comment to multi-gitter close so that it can close a PR with a comment indicating why it was closed

My use case
I want to supersede Pull Requests with new ones with different branch names. I want to be able to close the old PRs with a comment saying something along the lines of

Superseded by branch <branch_name>

[lindell]

I think this would be covered by the review command PR.

#332

[jtgrohn]

So the idea there would be to review then close?

The result would be similar I think, but it would be nicer to have the comment and pull request close timestamps be closer together. If I'm running multi-gitter on hundreds of repos, there would be a not insignificant delay between commenting and closing.

I'm looking to do the equivalent of

not comment and then click close

(note the Close button text change)