Merge pull request #4 from techdivision/master

Merge techdivision/master into wagnert/master
some minor annotation changes
mergin upstream changes
added missing attribute
added attribute initialisation
Merge pull request #11 from wick-ed/0.5.8-beta

refactored for pbc usage
Merge pull request #70 from wagnert/0.5.8-beta

Added missing attribute