Update the annotations of layers.py.

 Simpily demo, add paddle.default_main_program() and paddle.default_startup_program()

Feature/evaluator

Fix/reduce op

- Removed all main_program and startup_program in the demo.
- Using paddle.default_main_program() hides the implementation detail (e.g., using g_main_program) from the user, we can change the implementation in the future much easier.

* Adding greater than and less than equal ops to compare op
* Changing the name of the less_than_equal and greater_than_equal op
* Also changing the name of the functors

Remove some code to reduce the size of the mobile inference library.

fix pooling functor parameter order

Add dilation for exconv layer

max pool Layer with mask

* init commit

* change some dir name

Fix error in  networks' docstrings . 

* fix lod_tensor_array

* init test beam search decode op

* add test_beam_search_decode_op

Add Lod Reset Operator

* Conditional Block Forward

* Assign Operator.

Out=X, when type in [LoDTensor/SelectedRows/LoDTensorArray]

* Stash

* Add Scope::Rename

it is useful in gradient phase of an operator with block

* ConditionalBlock Grad Done

* Add comments

* yapf format code