title: Force WooCommerce to sell and ship to ONLY one state
body: <p>How do I force WooCommerce to sell and ship to only one state? 
  I can select a country but I can't find any way to allow selling and shipping only to one state/region.</p>
  
  <p>Let's say I've selected only Canada and I want to sell only in Ontario. How can I achieve that? I probably have to add something to function.php to filter the states, but I don't know where to look for it...</p>
  
  <p>Thanks!</p>