Feature: Limit number of Gists returned with `-l` flag

[zachriggle]

Being able to list all of my gists is neat! However, I don't always need all of them -- just the last few (or one, realistically).

It would be nice if -l took an optional numeric argument, for the number of Gists to fetch.

I understand that I can just do gist -l | head -5 to achieve the same effect, but it would be a neat small feature.