Preparations for an intermediate release 0.81

In the upcoming release 0.9, it is planned to simplify the installation procedure and the concept of the representer. This will include quite some changes in the code, and also at some points slightly change the interface. 
Before pushing these changes to the master, we should tag and release our improvements since 0.8, such that people can still use them without having to change their application immediately to the new API.