* Fix VS 2015 windows compilation: conversion from 'const unsigned int' to 'int' requires a narrowing conversion

* Missing new source file faceDetectorOpenCV.cpp in VS 2015 projects

* Fix VS 2015 windows compilation: conversion from 'const unsigned int' to 'int' requires a narrowing conversion

* first try on OpenCV face

* find a way to visualize detected face; enlarge by 1.5x

* revision for first-time pull request

* faceDetector

* fix little mistake

* Update headers.hpp

* Update CMakeLists.txt

* OpenCV face detector thread save & 4x faster

* Added doc

* Exposing first hand heatmaps through handExtractor

* Hand extractor exposes heatmaps for both hands of all detected persons.

* Clean-up hand heatmap code

* Face heatmap extraction similar to the hand-heatmap code

* Update faceExtractor.hpp

* Update faceExtractor.hpp

* Update handExtractor.hpp

* Update faceExtractor.cpp

* Update handExtractor.cpp

* Face heatmaps added to wrapper

* Added hand heatmaps to wrapper

* Cleaned code

* Added description in doc

* fix wrong json file format

COCO challenge only has 17 keypoints, so indexesInCocoOrder.size()==17.
openpose added the neck keypoint (index 1), therefore numberBodyParts==18.
numberBodyParts-1==17, Statement `if (bodyPart < numberBodyParts-1)` adds a comma for  every bodyPart ([0..16]), add a extra comma in the end, causing a bad json format file, which can not be proporly parsed.

* Update cocoJsonSaver.cpp