title: how to convert a dictionary containing iterables as items to a dataframe
body: <p>I have a dictionary d</p>
  
  <pre><code>d=dict()
  d['a']=2
  d['b']=3
  d['c']=list([1,5,7])
  </code></pre>
  
  <p>if I try to convert it using</p>
  
  <pre><code> pd.DataFrame.from_dict(d)
  </code></pre>
  
  <p>then I get</p>
  
  <pre><code>df=
  'a'     'b'     'c'
  2       3        1 
  2       3        5
  2       3        7
  </code></pre>
  
  <p>while I wanted:</p>
  
  <pre><code>df=
  'a'     'b'     'c'
  2       3        [1,5,7]
  </code></pre>
  
  <p>how to obtain this behavior? </p>