Attribute delegation

• A slightly more complex example:

has 'logger' => (
    is       => 'ro',
    isa      => 'My::Custom::Logger',
    required => 1,      
    handles  => { 
        write_to_log     => 'log',
        flush_log_output => 'flush',
    }
);

• The write_to_log and flush_log_output methods are added to the class
• delegating to the log and flush methods respectively