OpProto is a proto message that helps 3rd-party language bindings, e.g.
`Python`, to generate operator creation methods. The operator creation
method is the low-level API for 3rd-party language bindings. Op creation
methods take the user's input in that language, and convert users inputs
into `OpDesc` message, then passing that `OpDesc` message to Paddle's
C++ core and create an operator.

* A separated `attr_type.proto` is added, because that file wound
  be included by `op_desc.proto` in future.

enable users to set intial memory states for lstm/gru group.

Add pb_cc_library in generic.cmake

basic scope implementation #2629

* scope-impl

* refine GetOrCreateVariable

* refine code of scope with style check

* refine code of operator

* clang format

* move code to scope.h, remove scope.cc

* add Create for scope

* merge CreateVar and GetOrCreateVar

* do not use default argument in Scope

* update design doc

 Init partial network parameters from another saved model.

* add trainer library

* modifty file name

* move trainer to master client

* update

* update

* modify monitor master to receive a chan

* update

* use etcd client from etcd_client.go

* update

* update

* remove etcd client without lock

* update

* update the comment

* update commonts

fix xmap_readers and refine flowers dataset

Adding Enforce to platform

Add paddle::string::{F,S,}Printf

"fix client send empty gradients bug"

Rename paddle::strings::StringPiece into paddle::string::Piece

Memory CPU allocator

Make pserver able to get server index without etcd (decouple pserver with etcd)