* add LayerList insert and extend
test=develop

* add index range check
test=develop

* add sample codes
test=develop

* refine sample code
test=develop

* API(to_variable/save_dygraph) error message enhancement

* Involves AfsAPI to resolve slow downloading.
* Mainly used in PaddleBox

* error message enhancement for Conv2DTranspose, test=develop

* fix error_message, test=develop

* solve the conflict of ops with the same name. test=develop

* error message of NCE API enhancement

Fix the bug of matmul test_case

* fix no_grad signature
test=develop

* check func name instead of doc
test=develop

* Layer add training attr, add Dropout Layer

* add unit test for Dropout
test=develop

* minor fix
test=develop

* add missing args
test=develop

* support global flag in dropout, add docs
test=develop

* minor fix
test=develop

* minor fix
test=develop

* refine code comments
test=develop

* refine Dropout
test=develop

* fix ut
test=develop

* arg expansion
test=develop

* sample code update
test=develop

* prop -> p
test=develop

* fix ut
test=develop

* minor check fix
test=develop

* Remove the NGraph engine from PDPD repository
1. Each operator was removed from the operator's directory
2. Each test was removed from the unittest directory
3. The parallel executor support was removed from the PDPD
4. The CMake file was removed from the PDPD
5. The NG flags were removed from the repository
test=develop

* Remove ngraph from:
1. Cmake file
2. Python file
test=develop

* API(fluid.gridents) error message enhancement test=develop

* fix unitest failed test=develop

* fix init_gflags with 'python -c', test=develop

* fix pruned_program_cache_key of Operator, test=develop

* polish api program error message, test=develop

* fix condition error, test=develop

* fix test prune error, test=develop

* fix coverage problem, test=develop

* add Conv/ConvTranspose layers in paddle.nn.layer, test=develop

* add example code in docstring, test=develop

* update unittests to work with test_runner, test=develop

* Api (fluid.data/layers.data) error message enhancement. test=develop

* API (Switch) error message enhancement. 

* fix bug: dtype of out in api isfinite is set incorrectly. The dtype should be bool. 

* Op (Scope) error message enhancement test=develop

* support no_grad atomic operating
test=develop

* rm create param api
test=develop

* refine sample code
test=develop

* clean impl
test=develop

* add full_like op. test=develop

* add dygraph support. test=develop

* increase coverage. test=develop