I recently checked in some changes to the trunk that include docbook documentation (like Spring Framework's). If you are using subversion and have a trunk copy, update your copy. Then go to build.py, and execute:
This will generate three directories: target/docs/reference/html, target/docs/reference/html_single and target/docs/reference/pdf. In the first two, you will find an index.html file you can browse to. The third has a pdf file. All three of these represent the current official documentation for this project (albeit some is out of date).