- one test for type_id;
- another for comments in JSON;

a JSON emitter, a parser, tests and some basic doc.

There is an issue with processing of abs(short) function for
negative argument.

Affected OpenCL devices:
- iGPU: Intel(R) HD Graphics 520 (OpenCL 2.0 )
- CPU: Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz (OpenCL 2.0 (Build 10094))

GraphCutSeamFinderGpu requires cudalegacy.

  * avoid using vld1_f16 and vst1_f16 on gcc 4 series (Ubuntu 14.04)
  * guard correctly with #if
  * use static inline

* Common Canny parallelization added. TBB and single thread code removed. Final pass vectorized with SSE2 intrinsics.

* wrong #ifdef replaced with #if

* Merged to actual Canny version

* Merged common parallelized Canny with actual Canny implementation

* Remove 'Mutex *mutex' and pass 'Mutex mutex' from outside to parallelCanny

* Replaced extern Mutex with intern mutable Mutex.

  * stop using 'CUDA' prefix
  * add explanation

Problem is observed with test_loop_times=100
in corner cases like 93x1 or similar

- use `std::string` instead of `new char`;
- reserve 1 MB for buffer;