Corrected saving of default config file
Corrected loading of config file
Corrected joining of parts in CONFIGFILE
Updated to python 3.4
Small correction to skip a line
assert syntax correction
Added __init__ files for tests
Changed the whole logic of __iter__ and __getitem__

__iter__() and __getitem__ are false methods. They actually are class methods, which makes their definition on the fly quite tricky. The old solution would reassing the correct definition in the __init__ method. However, since it is a class method, it also affect other object (that might have a need of the other iterator or getter). Thus, the best way to make it work is the naive way that checks each time is dataset.target is None.
Changed test to remove errors when run.