title: Add native knitr print methods
body: <p>I'm looking for a way to adjust functions which usually show html tables in the viewer or browser in a way that they automatically insert the html in knitr documents like rnotebooks when called.</p>
  
  <p>Specifically I want to change the way functions in the package <a href="http://www.strengejacke.de/sjPlot/sjtbasics/#knitr-integration-of-html-tables" rel="nofollow noreferrer">sjPlot</a> behave. At the moment they return an object with a <code>$knitr</code> attribute that has to be inserted manually and then produce an html table in the viewer:</p>
  
  <pre><code>`r sjt.frq(efc$e42dep, no.output=TRUE)$knitr`
  </code></pre>
  
  <p>One of these functions is <a href="https://github.com/sjPlot/devel/blob/master/R/sjTabFrequencies.R" rel="nofollow noreferrer">sjt.frq</a>. Is there a way to do this?</p>