Add per driver Scanner and Valuer interface

[AlexisMontagne]

Description

Certain data type are not interpreted the same way in between different drivers.

The idea would be to:

• type assert the input values with an interface like interface { XxxValue() (driver.Value, error) }
• type assert the scanned values with an interface like interface { ScanXxx(interface{}) error }

It would bring two advantages:
1 - Allow a driver agnostic usage of Scanner/Valuer data types
2 - Use driver optimisation for certain data types (i.e. hstore in postgres etc...)

Acceptance Criteria

• Implement this semantic over backend/postgres
• Implement this semantic over backend/sqlite3