title: Sort by price low to high and high to low in product listing magento2
body: <p>I am new in Magento 2. I am using Magento 2.1.1</p>
  <p>I want to add custom <code>price low to high</code> and <code>price high to low</code> in Sort By dropdown in product listing page.</p>
  <p>I didn't get toolbar.phtml page. Also I didn't get any stuff regarding this in google.</p>