title: Next / Previous custom post type with custom field category
body: <p>I have custom post type "<strong>news</strong>" with custom field "<strong>category</strong>". In category user can select:</p>
  
  <ul>
  <li><p>0 - all</p></li>
  <li><p>1 - category1</p></li>
  <li><p>2 - category2</p></li>
  <li><p>3 - category3 </p></li>
  <li>4 - category4</li>
  </ul>
  
  <p>I need on single-news page next and previous link in same category, including the "<strong>all</strong>" category. So for example I'm on post <strong>X</strong> and it is in category <strong><em>3</em></strong>. Next post <strong>Y</strong> (ordered by date of that post) is in category <strong><em>0</em></strong> (all). If I click on next (page <strong>X</strong>) I should go on page <strong>Y</strong>, but there should be next link not in category <strong><em>0</em></strong> but in category <strong><em>3</em></strong>. </p>
  
  <p>Is it possible to do that? </p>