* initial commit

* fix error

* fix typo and order

* change from hgemm to gemmEx

* fix cpplint

* Fix cpplint errors in paddle/fluid/string

* Fix unit test error

* Correct

* Fix cpplint issues

* Fix cpplint issues in channel.h and channel_impl.h

* Fix typo

All leaves must be variables. When all variables are ready, the
execution will be completed. If a operator has no output, the `Op::Run`
might not be started when the execution of graph has been complete.