Set the version status to "-tp", for "technical preview".
compilation for windows
fixed typo
fixed cv::mixChannels OpenCL version
Update py_face_detection.rst

bug in example
Fix compiler error with Android NDK r8e

Original error without the fix:

opencv/modules/objdetect/src/cascadedetect.cpp: In member function 'bool cv::CascadeClassifierImpl::ocl_detectSingleScale(const cv::_InputArray&, cv::Size, int, double, cv::Size)':
/opencv/modules/objdetect/src/cascadedetect.cpp:1215:
error: no matching function for call to 'cv::ocl::Kernel::args(cv::ocl::KernelArg, cv::ocl::KernelArg, cv::ocl::KernelArg, int, cv::ocl::KernelArg, cv::ocl::KernelArg, cv::ocl::KernelArg, cv::Size&, int&, float, cv::Rect&, cv::Size&, cv::CascadeClassifierImpl::<anonymous enum>)'
Merge pull request #2102 from Nerei:compilatin_for_windows
Merge pull request #2103 from ilya-lavrenov:typo
Merge pull request #2116 from ilya-lavrenov:tapi_mixchannels_fix
Merge tag '3.0-ocl-tech-preview' (-s ours)
Merge pull request #2126 from yinghau76:master
Merge pull request #2119 from d-schmidt:patch-1