Allow to pull documents from another bucket using gaze & populate

[godric7]

We need to be able to get referenced data across buckets.

eg.

  var ct = require('couchtard');
  var bu_artists = new ct.Bucket({...});
  var bu_songs = new ct.Bucket({...});

  bu_artists.gaze('artists', 'songs_by_artist', {
    key: '/artists/1',  
    bucket: bu_songs
  }, function(err, songs, meta)) {
    console.log(songs); 
  });