title: Formatting mouse over labels in plotly when using ggplotly
body: <p>I am struggling with text formatting when using <code>ggplotly</code> and the mouse over functionality.</p>
  
  <pre><code>library(plotly)
  df &lt;- data.frame(a=letters, b=LETTERS, x=runif(26), y=runif(26))
  g &lt;- ggplot(df, aes(x,y)) + geom_point(aes(text=sprintf('letter: %s\nLetter: %s', a, b)))
  g
  (gg &lt;- ggplotly(g))
  </code></pre>
  
  <p>I would like to have some formatted text or at least a newline in my mouse over label. Is there a good documentation on how to design this mouse over bubble thing?</p>