title: Search with nested object: Can't get good syntax to get record I want
body: <p>I have this mapping for my publication model:</p>
  
  <pre><code>mapping do
      indexes :id, type: 'integer'
      indexes :publisher_id, type: 'integer'
      indexes :state
      indexes :title
      indexes :created_at, type: 'date'
      indexes :updated_at, type: 'date'
      indexes :formats, type: 'nested' do
          indexes :pid, type: 'integer'
          indexes :key_type
          indexes :value, type: 'string', analyzer: 'whitespace'
          indexes :state
          indexes :protection
          indexes :nature
          indexes :start_sale_at, type: 'date'
          indexes :issued_on, type: 'date'
          indexes :format_aliases do
              indexes :value, analyzer: 'whitespace'
          end
          indexes :cost do
              indexes :id, type: 'integer'
              indexes :country
              indexes :format
              indexes :amount, type: 'integer'
          end
      end
      indexes :collections do
          indexes :collection_id, type: 'integer'
          indexes :collection_title
      end
      indexes :contributors do
          indexes :contributor_id, type: 'integer'
          indexes :contributor_first_name, analyzer: 'whitespace'
          indexes :contributor_last_name, analyzer: 'whitespace'
      end
  end
  </code></pre>
  
  <p>I want to get all publication where state is not 'destroyed', and where one of the format nature is of type 'epub' and with a state set to 'sell'. </p>
  
  <p>I can get none destroyed publication doing this</p>
  
  <pre><code>tire.search do
      query do
          boolean do
              must_not {term :state, 'destroyed'}
          end
      end
  end
  </code></pre>
  
  <p>I can get all publication having a format where state is 'sell' and nature is 'epub' by doing this:</p>
  
  <pre><code>tire.search do
      nested path: 'formats' do
          query do
              match 'formats.nature', 'epub'
              match 'formats.state', 'sell'
          end
     end
  end
  </code></pre>
  
  <p>but I can't merge both together to get the complete solution.</p>