title: Extended regression lines with seaborn regplot
body: <p>I searched but I did not find the answer regrading the seaborn library. I also checked the documentation for <code>lmplot()</code> and <code>regplot()</code>, but did not find either.
  Is it possible to extend and control the length of regression lines? By default seaborn fits the length of regression line according to the length of x axis. Another option is to use  argument <code>truncate=True</code> - that would limit the regression line only to the extent of data.
  Other options?</p>
  
  <p>In my example I want the lower regression line to be extended down till x=0. And the upper line extended till the intersection with the lower one.</p>
  
  <p><img src="https://i.stack.imgur.com/0emM3.png" alt="example"></p>
  
  <pre><code>import matplotlib.pyplot as plt
  import pandas as pd
  import seaborn as sns
  
  file = 'cobbles.csv'
  df = pd.read_csv(file, sep=',')
  
  sns.regplot(x='downward_temp', y='downward_heat', data=df, ci=None)
  sns.regplot(x='upward_temp', y='upward_heat', data=df, ci=None, order=2)
  
  
  plt.xlim([0,25])
  plt.ylim([0,100])
  plt.show()
  </code></pre>