Fixed variable name consistency

The function parameters were different from the ones described below.

P.S. Why is ``flow`` InputOutputArray, shouldn't it be just OutputArray? If so, shouldn't the reason be specified - e.g. so others can benefit as well (e.g. not allocating memory on every frame?)
Documenting imgproc module

- disabled doxygen tree
- enabled doxygen enum listing
- added imgproc reference to main page
- enabled BiB support
- chenged doxygen root page format
Fix compilation when building without the Video I/O module.
Fix incorrect size computation
Updated Documentation (HoughCircles)

Rewrite the note on HoughCircles documentation to make it more clear

Add note to clarify that the output vector of found circles is sorted by
descending order of centres accumulator values.

Also delete reductant lines on the HoughCircles documentation.

Added comments to hough circles function.

Added comments to icvhoughgradient

Misalignment in line 1183 corrected
Update py_colorspaces.rst

mask = cv2.inRange(hsv, lower_green, upper_green)
to
mask = cv2.inRange(hsv, lower_blue, upper_blue)
Parallize building kmeans index in flann
- Use cv::Mutex to safely update converged flag
- Use cv::AutoBuffer rather than new allocation
- Fix "assignment operator could not be generated" warning
Fix "assignment operator could not be generated" warnings
samples: gpu: fix include of TickMeter
bug fix for a crash when input image is small
Make Ctrl+S open save dialog on Windows
fix gpu sample performance test cpu part
Merge pull request #3466 from taka-no-me:ctrl_s_win
Merge pull request #3457 from burun:patch-1
Merge pull request #3464 from asuwend1:master
Merge pull request #3458 from thorikawa:kmeans-index-parallel
Merge pull request #3467 from Dikay900:fix_gpu_surf_perf_test_cpu_part
Merge pull request #3446 from pokeefe:fix-compilation-without-videoio
Merge pull request #3426 from mshabunin:doxygen-imgproc