title: numpy genfromtxt converters unknown number of columns
body: <p>I have several data numeric files in which the decimal separator is a comma. So I use a lambda function to do a conversion:</p>
  
  <pre><code>import numpy as np
  def decimal_converter(num_cols):
      conv = dict((col, lambda valstr: \
      float(valstr.decode('utf-8').replace(',', '.'))) for col in range(nb_cols))
      return conv
  
  data = np.genfromtxt("file.csv", converters = decimal_converter(3))
  </code></pre>
  
  <p>the data in the file is like this:</p>
  
  <pre><code>0; 0,28321815;  0,5819178
  1; 0,56868281;  0,85621369
  2; 0,24022026;  0,53490058
  3; 0,63641921;  0,0293904
  4; 0,65585546;  0,55913776
  </code></pre>
  
  <p>Here with my function <code>decimal_converter</code> I need to specify the number of columns my file contains. Normally I don't need to specify <code>numpy.genfromtxt</code> the number of columns in the file and it takes all it finds. I would like to keep this feature even when using converters option. </p>