Title   : register_driver
 Usage   : $factory->register_driver("genscan", "Bio::Tools::Genscan");
 Function: Registers a driver a factory class should be able to instantiate.

           This method can be called both as an instance and as a class
           method.

 Returns : 
 Args    : Key of the driver (string) and the module implementing the driver
           (string).

 Title   : driver_table
 Usage   : $table = $factory->driver_table();
 Function: Returns a reference to the hash table storing associations of
           methods with drivers.

           You use this table to look up registered methods (keys) and
           drivers (values).

           In this implementation the table is class-specific and therefore
           shared by all instances. You can override this in a derived class,
           but note that this method can be called both as an instance and a
           class method.

           This will be the table used by the object internally. You should
           definitely know what you're doing if you modify the table's
           contents. Modifications are shared by _all_ instances, those present
           and those yet to be created.

 Returns : A reference to a hash table.
 Args    :

 Title   : get_driver
 Usage   : $module = $factory->get_driver("genscan");
 Function: Returns the module implementing a driver registered under the
           given key.
 Example : 
 Returns : A string.
 Args    : Key of the driver (string).

 Title   : _load_module
 Usage   : $self->_load_module("Bio::Tools::Genscan");
 Function: Loads up (like use) a module at run time on demand.
 Example : 
 Returns : TRUE on success
 Args    :