Add simple versioning to ActiveRecord models (TISS version). Each model has a to-many model named mymodel_h which records all changes (including destroys but not deletes) made to the model. This is the version used by http://tiss.tuwien.ac.at and substantially differs from the original version. If you want to use acts_as_versioned in your project we recommend to use technoweenie's version (can be found also on github)