title: Auto adjust font size in seaborn heatmap
body: <p>when using seaborn heatmap, is there a way to auto-adjust the font size for it to fit exactly inside the squares?
  for example in: </p>
  
  <pre><code>sns.heatmap(corrmat, vmin=corrmat.values.min(), vmax=1, square=True, cmap="YlGnBu", 
          linewidths=0.1, annot=True, annot_kws={"size":8})  
  </code></pre>
  
  <p>here the size is set in "annot_kws". </p>