title: Django-filter | Boolean fields
body: <p>I'm using django-filter package and I have many boolean fields.
  Is there a way to filter only when field is True? And show all other posibilities?</p>
  
  <p>For example if I have 3 fields: True, False, False... Render objects that have 1st field equal True but doesn't matter about de rest, don't consider it False.</p>
  
  <p><strong>model.py</strong></p>
  
  <pre><code>class Product(models.Model):
      name = models.CharField(max_length=15)
      is_dangerous = models.BooleanField()
      is_secret = models.BooleanField()
      is_active = models.BooleanField()
  </code></pre>
  
  <p><strong>filters.py</strong></p>
  
  <pre><code>class SearchFilter(django_filters.FilterSet):
      name = django_filters.CharFilter(lookup_expr='icontains')
      class Meta:
          model = Product
          fields = ['name', 'is_dangerous', 'is_secret', 'is_active',]
          filter_overrides = {
              models.BooleanField: {
                  'filter_class': django_filters.BooleanFilter,
                  'extra': lambda f: {
                      'widget': forms.CheckboxInput,
                  },
              },
          }
  </code></pre>
  
  <p><strong>urls.py</strong></p>
  
  <pre><code>url(r'^products/$', views.products, name='products')
  </code></pre>
  
  <p>When I enter to <code>products/</code> for the first time, I only see products that has all boolean fields = False and I want to see ALL products.</p>