* Changed plus operator to os.path.join()

* Remove '/' from PATH

When building OpenCV as a sub-project using cmake's add_subdirectory()
the OpenCV's build options would be overwritten to its default
state. With cmake 3.13+ the CMP0077 policy, option() honors previous
definitions via set().

- some of `icvCvt_BGR*` functions have R with B channels
  swapped what leads to the wrong conversion
- renames misleading `rgb` variable name to `bgr`
- swap back the conversion coefficients, `cB` should be the first
Signed-off-by: Janusz Lisiecki <jlisiecki@nvidia.com>

backport commit 659ffadd

Add explicit size check for Rodrigues() function to prevent issue like https://stackoverflow.com/questions/58969553

* doc: added macOS installation guide

* doc: added clarification and corrections

* docs: introduction entry, lowercase file names and ids

* imgproc(test): resize(LANCZOS4) reproducer 16192

* imgproc: fix resize LANCZOS4 coefficients generation

* cuda_mog2_issue_5296

* Fix #16007 - colinearity computed using all 3 coordinates

* calib3d(test): estimateAffine3D regression 16007