title: Getting feature names from within a FeatureUnion + Pipeline
body: <p>I am using a FeatureUnion to join features found from the title and description of events:</p>
  
  <pre><code>union = FeatureUnion(
      transformer_list=[
      # Pipeline for pulling features from the event's title
          ('title', Pipeline([
              ('selector', TextSelector(key='title')),
              ('count', CountVectorizer(stop_words='english')),
          ])),
  
          # Pipeline for standard bag-of-words model for description
          ('description', Pipeline([
              ('selector', TextSelector(key='description_snippet')),
              ('count', TfidfVectorizer(stop_words='english')),
          ])),
      ],
  
      transformer_weights ={
              'title': 1.0,
              'description': 0.2
      },
  )
  </code></pre>
  
  <p>However, calling <code>union.get_feature_names()</code> gives me an error: "Transformer title (type Pipeline) does not provide get_feature_names." I'd like to see some of the features that are generated by my different Vectorizers. How do I do this?</p>