Make CTC align op support for empty output

disable nccl and parallel_do test

Add target assigner operator for SSD detection.

make inference_lib_dist for fluid inference shared library

adjust the structure of documentation

Fundamental Data Reading in C++

* refine get cfgs method in memory optimization transpiler

* clean code

* It will sightly faster compile and make warpctc compile
well on CUDA 9 and GCC 5.5

Impl scalar switch case op with condition op

* set up python code

* fix bug

* add cc file

* fix cmake

* add inference test for label semantic role

* fix

* address comments

* address comments

* address comments

* address comments

* add use_cuda

* Adding panic logic and test case

* Change panic behavior to boolean instead of exception

* Adding atomic

* Switch to boolean

* Fix spacing

* Add to close method

* Add test case to return zero on a closed channel

* Rename method

* Fix test

* ReceiveFromBufferedChannelReturnResidualValuesTest

* Adding the variable and case for unbuffered channel

* Fix review comments

* Fix format

* Remove a zero-value comparison

* First basic implementation

* Add infer example for image_classification

* Address review comments: round 1

Add RunAndGetException in threadpool

Refine buffer receive

Change the behaviour of thread pool. Thread pool will ignore the
thrown exception implicitly. It is hard to debug.
Corrently, ThreadPool::Run will invoke `LOG(FATAL)` if an exception
thrown.