* 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.