[jhc] github mirror

This may have already existed, but I have been keeping a local git mirror of the darcs repository, and I decided to go ahead and publish it to github. So if anyone prefers to use git instead of darcs, by all means you are welcome to use my mirror. If you want to contribute new code, please keep it in a separate branch, so I can keep master in sync with John's tree. Thanks, https://github.com/jimcrayne/jhc