* Update Transformer using Paddle-1.6 apis.

* Add check_version for Paddle-1.6 and reorganize utils including check, configuration, etc.

Fix transformer inference when using ParallelExecutor by setting ExecutionStrategy to clear tensor array after each iteration. (#3374)

Fix the data file empty check.
Fix the utf8 file encoding.
Refine the README.

* Update transformer to be unified

* To support CE when unifing Transformer