Oneboxes links to Github repos, issues or pull requests in Chat
This userscript will automatically detect new and existing messages in chat that link to Github and onebox them, just like it is done already for posts on SE sites. Inspired by One-box repositories, issue tickets and such on GitHub in the chat on Meta.
Issues will also show the milestone, labels and assignee in version 1.1.
I recommend you use a userscript manager such as Greasemonkey or Tampermonkey because they make it much easier for you to manager userscripts.
Feature requests and bug reports are welcome as issues at the Github repo. Pull requests are even more welcome! ;)
You can test it in any chat room, or in the Sandbox; just like I did :)
I posted this on Code Review to get it reviewed and have updated the script after receiving some tips on improvement! :)