reformatted the documentation

* issue-16736: quick step towards moving SIFT from non-free to free. Moves
include, tests, and implementation to free area.

* FREAK : better rounding off for weighted dx and dy of orientation pairs

* updated using cvRound

* cvRound modified

* Add overload method and fix typos in omnidir (1/2)

Addresses part of https://github.com/opencv/opencv/issues/16601

* Add overload method in omnidir (2/2)

Addresses part of https://github.com/opencv/opencv/issues/16601

* fixed typo

* fixed document

Fixes error occurs in cv::ppf_match_3d::ICP::registerModelToScene()

* corrected out of range error

* remove unnecessary changes

* fix warning

Update test_hdr.cpp

Update test_hdr.cpp

Harmonise bibtex formatting. Sort entries alphabetically by the last name of the first paper author.

* ximgproc(test): createSuperpixelSLIC smoke test

* ximgproc: don't use 'operator+()' with empty cv::Mat

backport commit 13f76375

backport commit 8c092493

Added constructors and destructors for RgbdPlane

* declared constructors and destructors of RgbdPlane

* definitions written

* tests for python bindings added

Add test for ximgproc/edgeboxes and fix up Python sample to work with returning scores

* Test for Edgeboxes implementation

* Fix and enhance edgeboxes_demo.py

* Make double literal a float literal

* Address review feedback