Setters should return themselves to allow method chaining

Multiple setter method calls can be chained together by returning `$this` from each setter method.

For example, we can take code that looks like this:

    $object->setFirstName('John');
    $object->setLastName('Smith');
    $object->setPhoneNumber('123-456-7890');

And simplify it to something like:

    $object
        ->setFirstName('John')
        ->setLastName('Smith')
        ->setPhoneNumber('123-456-7890');