avoid no __exit__ attribute for python 2.6

This [issue has been fixed in python
2.7](http://bugs.python.org/issue5511) but for python 2.6
ZipFile object is not compatible with with_statement : it raises
AttributeError: ZipFile instance has no attribute ‘__exit__”
basic example

to answer @frenet on his request xmindltd/xmind-sdk-python#2
drop blank lines
add relationship
Merge pull request #6 from brumar/master

avoid no __exit__ attribute for python 2.6 and add Basic Example