* Added a mall note describing BUILD_opencv_world cmake option to the Installation in Windows tutorial.

* Made slight changes in BUILD_opencv_world documentation.

* Update windows_install.markdown

improved grammar

- The size of second channel should be size[2] of output tensor,
- The Scalar should be {variance[0], variance[0], variance[0], variance[0]}
  for _variance.size() == 1 case.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

tested with NDK 17b (17.1.4828580)

resolves #12307

Some `CV_Assert`s changed to `CV_Assert_N`s according to https://github.com/opencv/opencv/issues/12304

* Support Mask-RCNN from TensorFlow

* Fix a sample