Refine the readme.md of DSSM.

use clang_format having the same version with the Paddle main repo.

remove the useless directory for c-api.

Update the CTR image and description.

Fix README of nce_cost.

fix ci.

The new image is a courtesy of Varun

Fix the output of cnn in DSSM.

fix urls in nmt_without_attention's doc

Fix resnet_cifar10 in image_classification.

Update README.md

root README.cn.md point to the README file with specific language.

recover the READEME.cn.md for CTR

Redirect ds2 in README.

Fix the default model saving dir in NER.

Add tf2paddle to convert TensorFlow models to PaddlePaddle models.

Reorganize codes of LTR.

delete obsolete annotations of conv_seq2seq.