title: Iterate over all keys of nested map
body: <p>Given:</p>
  
  <pre><code>{:o {:i1 1
       :i2 {:ii1 4}}}
  </code></pre>
  
  <p>I'd like to iterate over the keys of the map in "absolute" form from the root as a vector. So I'd like:</p>
  
  <pre><code>{
   [:o :i1] 1
   [:o :i2 :ii1] 4
  }
  </code></pre>
  
  <p>As the result. Basically only get the leaf nodes.</p>