* "fix decode bug"

* "follow commnet"

* "fix error"

* "fix hook bug"

* fix based comment

* fix copyright

* fix based on comment

* Fix bug in MergeModel.cpp.

* Add a c-api inferface to initilize the thread environment of Paddle and add a GPU example.

* Add some note for paddle_init_thread and move the inplementation of paddle_error_string into a .cpp file.

* Add some comments.