This add-on (in common with all of my ExpressionEngine add-ons) is not officially supported.
The source code is reasonably well-documented, and you are free to fork the repo if you'd like to make some changes or improvements (it's distributed under a liberal open source license).
Hopefully this will be everything you need to use this add-on in your projects, but if not please don't email me asking for support; I don't even have ExpressionEngine installed locally any more.
Extension demonstrating how to use the campaigner_subscribe_start hook, available as of Campaigner version 4.0.0.