Follow a related resource

Add a `.follow(relationship)` method to the response promise.

The relationship to follow may be define as a plain string, an object
with the rel and params, or an array containing one or more entries with
the previous forms.

Examples:
    response.follow('next')

    response.follow({ rel: 'next', params: { pageSize: 100 } })

    response.follow([
        { rel: 'items', params: { projection: 'noImages' } },
        'search',
        { rel: 'findByGalleryIsNull', params: { projection: 'noImages' } },
        'items'
    ])