In her latest post Lorna Mitchell has shared some scripts she uses to automate the creation of a changelog based on the GitHub issue comments and fixes.
My current project does periodic releases, we build a few things, then we work on getting a bunch of user feedback and changing/fixing things before we actually release. [...] When a branch merges in to the main line, we use the "fixes #42" notation to simultaneously close off the issue that it relates to. This has been working pretty well, and today I got the question "what's new since I last saw this project?" - so I created a changelog. It's rather rough-and-ready but I had fun so I thought I'd share.
The script operates off of a local git cloned version of the repository and grabs all commit messages with the tern "fixes" in it. The script then takes the log file, matches the issue ID and then makes a cur call out to the GitHub API to get that issue's description. This is then taken, formatted and dropped into the output.