Add issues command, which opens github issues for a repo

Just came up with this command, I think it's gonna be great!

While you're in a git repo on your command line, you run `issues` and it opens the github issues for that repo in your browser.
I guess the question is whether this repo is a collection of scripts or a framework for building out shared git tools within our group. If I were to post this script on the [github subreddit](http://www.reddit.com/r/github), for example, there would be a much lower barrier to installing if it were a small, self-contained script that didn't require `.bashrc` changes.