Merge pull request #15371 from Wenzhao-Xiang:gsoc_2019

[GSoC 2019] Improve the performance of JavaScript version of OpenCV (OpenCV.js)

* [GSoC 2019]

Improve the performance of JavaScript version of OpenCV (OpenCV.js):
1. Create the base of OpenCV.js performance test:
     This perf test is based on benchmark.js(https://benchmarkjs.com). And first add `cvtColor`, `Resize`, `Threshold` into it.
2. Optimize the OpenCV.js performance by WASM threads:
     This optimization is based on Web Worker API and SharedArrayBuffer, so it can be only used in browser.
3. Optimize the OpenCV.js performance by WASM SIMD:
     Add WASM SIMD backend for OpenCV Universal Intrinsics. It's experimental as WASM SIMD is still in development.

* [GSoC2019] 

1. use short license header
2. fix documentation node issue
3. remove the unused `hasSIMD128()` api

* [GSoC2019]

1. fix emscripten define
2. use fallback function for f16

* [GSoC2019]

Fix rebase issue

modules/core/include/opencv2/core/cv_cpu_dispatch.h

@@ -157,6 +157,11 @@
 #  define CV_MSA 1
 #endif
 
+#ifdef __EMSCRIPTEN__
+#  define CV_WASM_SIMD 1
+#  include <wasm_simd128.h>
+#endif
+
 #endif // CV_ENABLE_INTRINSICS && !CV_DISABLE_OPTIMIZATION && !__CUDACC__
 
 #if defined CV_CPU_COMPILE_AVX && !defined CV_CPU_BASELINE_COMPILE_AVX
@@ -328,3 +333,7 @@ struct VZeroUpperGuard {
 #ifndef CV_MSA
 #  define CV_MSA 0
 #endif
+
+#ifndef CV_WASM_SIMD
+#  define CV_WASM_SIMD 0
+#endif

modules/core/include/opencv2/core/hal/intrin.hpp

@@ -168,7 +168,7 @@ using namespace CV_CPU_OPTIMIZATION_HAL_NAMESPACE;
 #   undef CV_MSA
 #endif
 
-#if CV_SSE2 || CV_NEON || CV_VSX || CV_MSA
+#if CV_SSE2 || CV_NEON || CV_VSX || CV_MSA || CV_WASM_SIMD
 #define CV__SIMD_FORWARD 128
 #include "opencv2/core/hal/intrin_forward.hpp"
 #endif
@@ -190,6 +190,9 @@ using namespace CV_CPU_OPTIMIZATION_HAL_NAMESPACE;
 
 #include "opencv2/core/hal/intrin_msa.hpp"
 
+#elif CV_WASM_SIMD
+#include "opencv2/core/hal/intrin_wasm.hpp"
+
 #else
 
 #define CV_SIMD128_CPP 1