As the title

* add WeightedRandomSampler. test=develop

* add paddle.io.ComposeDataset & paddle.io.ChainDataset. test=develop

* init commit of new save/load

* fix failed unittests

* fix save_load_v2 unittest failed

* fix failed unittest & polish doc

* add tests for coverage

* add more tests & move static apis

* fix example code error

* polish emample code

* fix detail example code problem

* remove paddle.readers API. test=develop

* Move hapi form paddle/incubate to paddle

* Remove vision/datasets/utils.py and clean code

* Add sample code for conll05

* Print pull path when saving model

* Fix sample code after paramter_list of SGD is changed to parameters

* Fix bug in wmt16 datase

* add TensorDataset. test=develop

* add Sampler/SequenceSampler/RandomSampler. test=develop

* add IterableDataset support in multiprocess DataLoader. test=develop

* add base name alias; test=develop

* fix embedding bug; test=develop

* fix io error; test=develop

* add metric; test=develop

* add import palce; test=develop

* add setup; test=develop

* fix incubate reader; test=develop

* fix initializer error; test=develop

* add DataLoader, Dataset, BatchSampler