I started maintaining a website a Moodle Xref (Cross ref site) and differences site a few years back as I find myself having to deal with different versions of Moodle in my role. I still maintain and use it despite having a reasonable IDE especially when I want to quickly view the differences between Moodle versions some of the core code. I have just updated it and it currently versions 2.9 to 3.8 are covered. It may be useful to some other plugin developers so you can view it at http://xref-diff.mukudu-dev.net/. Hope this proves useful, it gets a few hundred hits a month currently.
Thank you very much for that work.