title: Django-filter with DRF - How to do 'and' when applying multiple values with the same lookup?
body: <p>This is a slightly simplified example of the filterset I'm using, which I'm using with the DjangoFilterBackend for Django Rest Framework. I'd like to be able to send a request to <code>/api/bookmarks/?title__contains=word1&amp;title__contains=word2</code> and have results returned that contain both words, but currently it ignores the first parameter and only filters for word2. </p>
  
  <p>Any help would be very appreciated!</p>
  
  <pre><code>class BookmarkFilter(django_filters.FilterSet):
  
      class Meta:
          model = Bookmark
          fields = {
              'title': ['startswith', 'endswith', 'contains', 'exact', 'istartswith', 'iendswith', 'icontains', 'iexact'],
          }
  
  class BookmarkViewSet(viewsets.ModelViewSet):
      serializer_class = BookmarkSerializer
      permission_classes = (IsAuthenticated,)
      filter_backends = (DjangoFilterBackend,)
      filter_class = BookmarkFilter
      ordering_fields = ('title', 'date', 'modified')
      ordering = '-modified'
      page_size = 10
  </code></pre>