[7.0] [ADD] 'document extract from database'

Hi, 

I propose a module developped by Julius Network Solution, I got here http://bazaar.launchpad.net/~julius-network-solutions/julius-openobject-addons/7.0/files.

I did some refactoring (flake8, Pylint, adding tests)

Coverage: 93%.

Note: Travis fails for Pylint bugs in other modules.

Thanks for your review.
Why is there write_again and _write_again ?