title: Convert Numpy array of ASCII codes to string
body: <p>I would like to convert a NumPy array of integers representing ASCII codes to the corresponding string.
  For example ASCII code 97 is equal to character <code>"a"</code>. 
  I tried:</p>
  
  <pre><code>from numpy import *
  a=array([97, 98, 99])
  c = a.astype('string')
  print c
  </code></pre>
  
  <p>which gives:</p>
  
  <pre><code>['9' '9' '9']
  </code></pre>
  
  <p>but I would like to get the string <code>"abc"</code>.</p>