title: Flextable : using superscript in the dataframe
body: <p>This question was asked few times, but surprinsingly, no answer was given.</p>
  
  <p>I want some numbers in my dataframe to appear in superscript.
  The functions <code>compose</code> and <code>display</code> are not suitable here since I don't know yet which values in my dataframe will appear in superscript (my tables are generated automatically).</p>
  
  <p>I tried to use <code>^8^</code>like for <code>kable</code>, <code>$$10^-3$$</code>, <code>paste(expression(10^2))</code>,  <code>"H\\textsubscript{123}"</code>, etc.</p>
  
  <p>Nothing works !! Help ! I pull out my hair...</p>
  
  <pre><code>library(flextable)
  bab = data.frame(c( "10\\textsubscript{-3}", 
  paste(as.expression(10^-3)), '10%-3%', '10^-2^' ))
  flextable(bab)
  </code></pre>
  
  <p>I am knitting from <code>R</code>to html.</p>