title: Shuffling tfrecords files
body: <p>I have 5 tfrecords files, one for each object. While training I want to  read data equally from all the 5 tfrecords i.e. if my batch size is 50, I should get 10 samples from 1st tfrecord file, 10 samples from the second tfrecord file and so on. Currently, it just reads sequentially from all the three files i.e. I get 50 samples from the same record. Is there a way to sample from differnt tfrecords files?</p>