I was looking for LensKit 3.0-T5 API but I only found LensKit 3.0-SNAPSHOT API. So what's the relationship between LensKit 3.0-SNAPSHOT and 3.0-T5 (or any other 3.0-T* versions)?
My guess is that 3.0-SNAPSHOT is the API that describes quite accurately any of the 3.0-T* versions. If not, which updated, well-documented version of LensKit should I implement?
T5 are 'teaching snapshots' (effectively milestone releases, but early in the 3.0 dev cycle) of 3.0. 3.0-SNAPSHOT has seen quite a few changes since -T5. T1-5 are pretty similar to each other, mostly bug fixes between them.
You can find documentation for the -T series here: http://mooc.lenskit.org/
You can also find current -SNAPSHOT JavaDoc here: http://lenskit.org/master/apidocs/
[current as of 7/12/2016] We expect to make a -T6 release within the next week that contains the current 3.0-SNAPSHOT code, and will be updating the teaching site accordingly. I hope to be able to cut the final 3.0 release - and update the http://lenskit.org web site - by mid August.
I would recommend either 2.2.1 or -SNAPSHOT, planning to upgrade to -T6 or 3.0 final.