* update api 1.8

* update model 1.8

* fix save error of xdeepfm
* test=develop

* upgrade dcn and xdeepfm, change from all old save/load api to fluid.save and fluid.load
* test=develop

* reset auc more elegant and fix bug and README in ctr/dnn

* change ctr/dnn README

* fix apis, including os.path, shell and multiprocess

* use mul.cpu_count in win

* PaddleRec release 1.6 api update

* Update README.md

* Update README.md

bold remind of paddle version

* Update README.md

change paddle version note

* fix deepfm failed in 2*1 local distributed training

* fix deepfm preprocess bug

* fix deepfm preprocess bug and README

* PaddleRec xdeepfm add local distributed training

* PaddleRec deepfm dcn add local distributed training

* change PaddleRec deepfm README.md

* add embedding is_sparse flag in argparser

* fix deepfm failed in ver 1.5.2 when use transpiler

* fix xdeepfm failed in ver 1.5.2 when use transpiler

* fix some bugs in dnn deepfm and dcn

* fix embedding size in deepfm

add xDeepFM, DCN model in PaddleRec/ctr.
change DeepFM data download script.