title: Check if a hash's keys include all of a set of keys
body: <p>I'm looking for a better way to do</p>
  
  <pre><code>if hash.key? :a &amp;&amp;
     hash.key? :b &amp;&amp;
     hash.key? :c &amp;&amp;
     hash.key? :d
  </code></pre>
  
  <p>preferably something like</p>
  
  <pre><code>hash.includes_keys? [ :a, :b, :c, :d ] 
  </code></pre>
  
  <p>I came up with </p>
  
  <pre><code>hash.keys &amp; [:a, :b, :c, :d] == [:a, :b, :c, :d]
  </code></pre>
  
  <p>but I dont like having to add the array twice though</p>