* Add distributed implementation for recommender system

* Addressing code review feedback

* remove pick dependency

* fix bug

* small fix

* modify executor.py for save and load

* clean code

* Add usage example

* refine executor run function

* fix bug

* refine executor code

* fix block bug

* fix comments

* fix bug

* fix pass num

Unify the recognize_digits

The English of the previous API is bad.

* Adding the distributed implementation for machine translation

* re-running CI

* Updated the code style

neural machine translation model support beam search with while op

* limit variable type to lod tensor in memory optimization transpiler

* refine policy

* support while operator

* fix random seed and training data order

* refine get_cfgs method to support multi while operators

* refine codes

2. Fix evaluator using 'reduce_sum' op instead of 'mean' op

* add memory optimization transpiler demo

* add memory benchmark compile option

* add gflags instead of macro

* refine code