* add isort config

* isort all files

* [CodeStyle][py2][U008] remove unnecessary args in `super()`

* remove remained args

* revert changes in test_pylayer_op

* Revert "revert changes in test_pylayer_op"

This reverts commit ff185a9ae738afac3b0264f61bde6c6b7f72e7c4.

* revert some changes in example code

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* tempfile_fix

* update

* fix_CI

* update_word2vec.inference.model

* remove_change_in_word2vec_book

* fix_word2vec_book

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* fix dtype of ungenerated grad var

* update ut

* refine code

* set default dtype

* fix could_use_cudnn bug

* remove debug code

* re-implement

* fix bug

* fix wmt14 doc, remove backward, add bidirect direction in rnn api

* fix rnn unittest

* fix test_rnn_nets_static.py bug

As the title

add two paddle-2.0 apis: paddle.static.io.save_inference_model and paddle.static.io.load_inference_model (#28606)

* add two apis: paddle.static.io.save_inference_model and paddle.static.io.load_inference_mode, which are campatible with paddle.fluid.io.save_inference_model and paddle.fluid.io.load_inference_model respectively.

* add unittest for new save_inference_model and load_inference_model. test=develop

* enhance doc. test=develop

* add paddle.enable_static() to test_inference_model_io.py. test=develop

* Add rnn_op.
test=develop

* Fix rnn_op grad maker's drop_empty_grad.
test=develop

* rename manual_seed to seed

* rename xxx1d-->xxx1D, xxx2d-->xxx2D, xxx3d-->xxx3D

* rename manual_seed --> seed

* do not rename .cc, .cu and .h file

* rename manual_seed --> seed

* rename manual_seed --> seed

* rename manual_seed --> seed

* rename manual_seed --> seed

* disable_static on doc example code

* donot change manual_seed on generator

* add enable_static on sample code

* convert python/paddle/fluid/layers/nn.py to bak

* fix typo

* fix code style

* fix seed to manual_seed when call functions of Generator()

* fix bug

* Incorporate cudnn_lstm into LSTM api.
test=develop

* Make coalesce_tensor support alignment optionally.
test=develop

* Reorganize RNN apis. test=develop

* Fix cudnn rnn layout conversion.
test=develop

* Add sequence_length support for RNN cudnn implement.
Add optional init_h and init_c gradient for cudnn_lstm_op.
test=develop

* Use create_parameter for rnn cudnn impl.
test=develop

* Move `self._flat_weight = self.create_parameter()` in RNNBase to main_program.
test=develop

* Update RNN api unittest to use set_device.
test=develop

* Fix set_place for unit tests of RNN apis.
test=develop

* Fix use_align in coalesce_tensor_op.
test=develop

* Adjust RNN apis arguments according to comments.
test=develop

* Polish documents for SimpleRNN apis.
test=develop

* Refine random seed in cudnn_lstm_op.
Expose rnn params from sublayers to RNN.
test=develop

* Fix RNN saving for jit.save.
Refine cudnn_lstm dropout behavior.
test=develop

* Fix doc of GRU. test=develop

* Use ShareDataWith to avoid copying for cudnn_lstm_op test.
test=develop

* Remove updates on cudnn_lstm temporarily.
test=develop

* Use ShareDataWith to avoid copying for cudnn_lstm_op test.
test=develop

* Refine random seed in cudnn_lstm_op.
test=develop

* Fix test_lstm by adjust ConcreteProgram buffer getter.
test=develop

* Use create_parameter instead of create_var for rnn._flat_weight for static graph usage.
test=develop

* Remove W input for cudnn_lstm to pass unused_var_check.
test=develop

* Add test_predict for RNN unit tests coverage.
test=develop

* Fix code style of rnn.
test=develop

* Fix F.rnn usage in rnn.py.
test=develop

* Makes the Bind Method more intelligent

* Makes the Bind Method more intelligent

* fix unittest

* fix unittest

* fix conflict

* Add RNN related apis in paddl.nn
test=develop

* new rnn api, cell almost done

* add new progresses in rnn APIs for 2.0

* refine rnn APIs and docstrings.

* add unittets

* disable gpu tests when paddle is not compiled with cuda support

* remove unnecessary imports

* fix docstring

* add to no_sample wlist

* backport to python2 to avoid yield from

* add **kwargs, fix typos

* update docstrings for birnn

* rename argument for SimpleRNN and SimpleRNNCell, fix sample code

* add default value for initial_states in fluid.layers.birnn
Co-authored-by: Nguosheng <guosheng@baidu.com>