title: How to have patterns for the color bar in Biokit/corrplot
body: <p>I wonder if it is possible with  corrplot (from the biokit package) to have a colobar with patterns.
  In this example below, for the colobar, I would like to have 5 bubbles with differents sizes associated to the matrix's values ([-1, -0.5, 0, +0.5, +1]).</p>
  
  <p>Ideas ?
  thanks a lot</p>
  
  <pre><code>import numpy as np
  import pandas as pd
  from biokit.viz import corrplot
  from matplotlib import pyplot as plt
  import string
  
  letters = string.ascii_uppercase[0:15]
  df = pd.DataFrame(dict(( (k, np.random.random(10)+ord(k)-65) for k in letters)))
  df = df.corr()
  
  c = corrplot.Corrplot(df)
  
  c.plot(colorbar=True, upper='circle', rotation=60, cmap='Oranges', fontsize=12)
  
  plt.tight_layout()
  plt.show()
  </code></pre>