Store the SVNblame information

[Peter Johansson]

ref #74
needed for #62

To be able to generate a blame output (#62) the File class must have access to the SVNblame object. Either it could be held in the Stats class or it could be held in the File class which seems to be a smoother design for allowing File to hold several different Stats objects without holding several (identical) SVNblame objects. Also, it must be possible to traverse through the container of information.