Introduce operators
Introduce operators

Final is THE word. Add some doc.

Fix Scrutinizer issues

Fix Scrutinizer issues

Fix Scrutinizer issues

Fix Scrutinizer issues

Create interfaces for filesystem and file factory, add default filesystem and factory and lazy factory

Remove userless old interface

Fix scrutinizer issues

Fix scrutinizer issues
Merge pull request #38 from Gaufrette/feature/operators

Introduce operators