title: ggplot geom_text accept markdown
body: <p>I'm trying to add a label to a ggplot graph using geom_text. I can add the label correctly, but I can't get the label to use markdown. I need the text to follow statistical conventions.</p>
  
  <pre><code>ggplot(diamonds, 
     aes(carat, price)) + 
     geom_point(alpha=0.1) +
     geom_smooth(method="lm") + 
     geom_text(size=2.5, aes(x = 4, y = 4,
                        label=paste("r^2=", 0.34, "\n",
                             "gradient= ", 0.56, "\n",
                             "_p_=", 0.003)))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/Zq0fr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Zq0fr.png" alt="output"></a></p>