* generic.cmake can propogate dependencies through libraries. It is no
  need to specific all dependencies.

update docs url

fix dynload link error: undefined reference dlsym

Network implement

Pserver Save state

update the md5sum of WMT14 trained model.

* add device_context

* add unittest for device_context

* transfer to use function paddle::platform::throw_on_error

* fix cuda build error

* using dynload functions

* follow comments

"lr state serialization"

Fix paddle build when it's a subdirectory of another project

Update comments of maxout_layer

mistaken: Folk -> Fork in develop branch

* init op_registry.h

* dev op_registry.h

* add 'attr_checker.h', which is a draft of op attribute checker.

* rename some macro parameters

* 1. Use `Attribute` and `AttributeMap` instead of `OpDesc`. `AttributeMap` is a unordered_map of <string, Attribute>, and `Attribute` is a boost::variant object to hold multiple types of attribute value.
2. Use `PADDLE_ENFORCE` to print checkers' fail message.
3. Abstract default value operations to a new function: `DefaultChecker`.

* rename DefaultChecker to DefaultValueSetter

ZZ

* Finish op_registry

1. Complete the development of interfaces between OpRegistry and
Protobuf.
2. Add unit test for op_registry.h

* Add demo and test of custome checker

* fix merge conflict

FIX: explicitly specify glog install path