Config instance has now to be passed to init() function.
Remove Condition:: property. It was bad code.
(Little) clean code of Condition, Where, Select and Relationship.
Merge branch 'cleaning'
Clean Condition::leftHandSide method
Cleaned Relationship class.
Clean some query classes.
New "group_by" option.
order_by option's syntax more flexible
Add comments in query classes.
Remove Singleton pattern for Database and Config classes. Use dependency injection, now. Much
cleaner.
Comment Relationship.
Update documentation
Debug