code: function ls(uri, callback) {
    if (!uri) {
      callback(new Error('uri is required'))
    }
    util.getAll(uri, function(err, val) {
      var res = {}
      for (var i=0; i<val.length; i++) {
        if (val[i].predicate.uri === 'http://www.w3.org/ns/ldp#contains') {
          if (! res[val[i].object.uri]) res[val[i].object.uri] = {}
          res[val[i].object.uri].contains = val[i].object.uri
        }
        if (val[i].predicate.uri === 'http://www.w3.org/ns/posix/stat#mtime') {
          if (! res[val[i].subject.uri]) res[val[i].subject.uri] = {}
          res[val[i].subject.uri].mtime = val[i].object.value
        }
  
      }
  
      var arr =[]
      for( var k in res ) {
        if (res.hasOwnProperty(k)) {
          if (k && res[k] && res[k].mtime && res[k].contains) {
            arr.push({ file : res[k].contains, mtime : res[k].mtime })
          }
        }
      }
  
      arr = arr.sort(function(a, b){
        if (a.mtime < b.mtime) return -1
        if (a.mtime > b.mtime) return 1
        return 0
      })
  
      var ret = []
      for (i=0; i<arr.length; i++) {
        ret.push(arr[i].file)
      }
  
      callback(null, ret)
    })
  }
docs: get the contents of a container as an array
  @param  {[type]}   argv     [description]
  @param  {Function} callback [description]
  @return {[type]}            [description]