title: Is there a simple way to iterate through pairs in a Ruby hash in order of addition (i.e. oldest first)?
body: <p>I create an empty hash <code>chickens</code>, and key-value pairs are then added over time.</p>
  
  <pre><code>chickens = {} 
  chickens.merge!("Davison"=&gt;"plucky")
  chickens.merge!("Mortimer"=&gt;"sullen")
  chickens.merge!("Chauncey"=&gt;"forlorn") 
  
  for name,mood in chickens do puts "#{name}: #{mood}" end
  </code></pre>
  
  <p>produces  </p>
  
  <pre><code>Mortimer: sullen
  Chauncey: forlorn
  Davison: plucky
  </code></pre>
  
  <p>but I don't desire this. How do I cycle through the chickens in the order they were added?</p>