Add breadcrumbs to Document API (issue #4)

Add breadcrumbs to Document API related to issue #4
And allowing to add multiple breadcrumbs (array) at once.

Instead of repeatly using `$this->document->addBreadcrumbs()` to add breadcrumb, allow to push an array

    $breadcrumbs    = array();
    $breadcrumbs[]  = array(
        'text' => $this->language->get('text_home'),
        'href' => $this->url->link('common/home', 'token=' . $this->session->data['token'], 'SSL')
    );
    $breadcrumbs[]  = array(
        'text' => $this->language->get('heading_title'),
        'href' => $this->url->link('catalog/product', 'token=' . $this->session->data['token'], 'SSL')
    );

    $this->document->addBreadcrumb($breadcrumbs);