title: r markdown (knitr::kable): not print repeated values
body: <p>When using <code>knitr::kable(tibble)</code> is there a way not to show values if they are repetitions?</p>
  <p>For example:</p>
  <pre><code>var1  var2  var3 
  ----------------
  A     C     1
  A     D     2
  A     E     3
  A     E     4
  B     C     1
  B     D     2
  B     E     3
  </code></pre>
  <p>Should be printed as:</p>
  <pre><code>var1  var2  var3 
  ----------------
  A     C     1
        D     2
        E     3
              4
        C     1
  B     D     2
        E     3
  </code></pre>