I know the source is on GitHub, but is there an issue tracker or any other development documentation for people who are interested in contributing?
You’re welcome discuss about issues here in the forum. At the moment, there’s no issue tracker because it has been (mis)used as a discussion and support platform (which clearly is not the purpose of an issue tracker). Also, we’ll probably move to another git hosting platform (Gitlab).
Unfortunately, there’s not much development documentation, but I try to add Javadoc (and tests) constantly.