When I downloaded the latest 2.5.x snapshot (2.5.12) and tried it, I ran into this problem: Can't find binding skeleton script
So I should better use version 3 for developing bindings, I think.
For 3.x (3.1.0) I get yet another error. I opened a new topic to describe it: Getting started with Development openHAB 3 - Why can't I access paperui?