Witold Jaworski released an updated version of his free book about coding add-ons for Blender, bringing it up to date with Blender 2.80. According to the the author "the book contains a practical introduction to the Blender Python API. It describes the process of writing a new add-on. I discuss in detail every phase of the implementation, showing not only the tools, but also explaining the methods that I use. " Download it from Witold's website.