title: format output data in pandas to_html
body: <p>I use pandas' to_html to generate output file, when data are written to the file they have many digits after the decimal point. The pandas' to_html float_format method can limit the digits, but when I used 'float_format' as below: </p>
  
  <pre><code>DataFormat.to_html(header=True,index=False,na_rep='NaN',float_format='%10.2f')
  </code></pre>
  
  <p>it raise a exception:</p>
  
  <pre><code>typeError: 'str' object is not callable
  </code></pre>
  
  <p>how to solve this problem?</p>