New DataZoomer db Module

The new db is now implemented in DataZoomer on an experimental basis. The db module is much lighter weight and faster than the current database module.

It achieves this by doing the minimum required to provide a useful database API and by making use of generators and fetchmany instead of fetchall as is done in the database module.

The db module will be most useful when dealing with very large databases or in instances when every bit of speed matters.

Additional modules are being developed to use the db module to provide high level functionality such as record and sparse key value storage.

This db new module will eventually replace the database module entirely.