title: Multiple replace
body: <p>Have:</p>
  
  <pre><code>"a__b_c_____d__e_f__"
  </code></pre>
  
  <p>Need:</p>
  
  <pre><code>"a_b_c_d_e_f_"
  </code></pre>
  
  <p>ie: Replace all the <code>"___"</code> substrings (1 or more underscores) with <code>"_"</code> (single underscore) <em>without loops</em>.</p>