Add float16 support to batch norm operator

Multi-pass reader

repair image link in rnn.md

Add an argument in Executor.Run to allow users to choose whether to create and destroy variables every time. (#9242)

Multi-threaded reader in C++

Fix a bug of RecordIO

change the path of image code

* Create select_op design document

* Fix pre-commit issues

* Update select op as per varun's comments

expose dilation to conv2d and bias/act to con2d_trans

Add float16 support to Elementwise Add op

Update index_en.rst

optimize executor.run

fix space and toctree format

Done

* Add RMSProp optimizer warpper.

* Follow comments.

pserver runs in parallel

fix #8956

repair image problem of en distributed training

1. add 1 sentence that was not translated in the original version
2. repair image showing problem

Add python wrapper for Adadelta optimizer

Enhance sequence_expand operator