The developer documentation in the website http://www.yafaray.org/development/documentation is horribly out of date respect to the current YafaRay v3 versions. It even mentions the GSOC 2010 and the API documentation at http://www.yafaray.org/development/developersfaq in ancient, from back 2009!!
I will try to update the documentation as much as possible, and to update the API documentation with the latest GitHub master code. For now, I've removed the GSOC information from the Table of Contents (I didn't delete the actual documents, only modified the table of contents so it does not mention it), and I've added a note saying that the developer documentation is outdated and needs to be updated.