* add new chessboard detector

The chessboar detector is based on the paper.
Accurate Detection and Localization of Checkerboard Corners for
Calibration Alexander Duda, Udo Frese
British Machine Vision Conference, o.A., 2018.

It utilizes point symmetry of checkerboard corners in combination with a
localized Radon transform approximated by box filters to achieve high
performance even on large images. Here, tests have shown that the
ability to localize checkerboard corners is close to the theoretical
limit of 1/100 of a pixel while being considerably less sensitive
to image noise than standard methods.

* chessboard: add reference to bibtex file

* chessboard: add dependency to opencv_flann

* fix: test chesscorners. It is valid to return an empty list

In case no chessboard was detected it should be valid for the detector
to return an empty list.

For simplifcation, it should be allowed to return any number of corners
if they are flagged as not found.

* fix: opencv.bib remove empty lines

* fix: doc findChessboardCorners replace cvSize with cv::Size

* chessboard tests: factor out logic selecting detector

* chessboard: add unit test for findChessboardCorners2

This is includes a new chessboard generator which supports subpix
corners with high accuracy by wrapping an optimal chessboard using
wrapPerspective.

* fix: chessboard unit test - overwrite of default parameter flag of findCirclesGrid

* chessboard: remove trailing whitespace

* chessboard: fix debug drawing

* chessboard: fix some issues during code review

* chessboard: normalize asymmetric chessboard

* chessboard: fix float double warning

* remove trailing whitespace

* chessboards: fix compiler warnings

* chessboards: fix compiler warnings

* checkerboard: some performance improvements

* chessboard: remove NULL macros for language bindinges from internal headers

* chessboard: shorten license terms

* chessboard: remove unused internal method

* chessboard: set helper functions to static

* chessboard: fix normalizePoints1D using unshifted points

* chessboard: remove wrongly copied text

* chessboard: use CV_CheckTypeEQ macro

* chessboard: comment all NaN checks

* chessboard: use consistent color conversion

* chessboard: use CheckChannelEQ macro

* chessboard: assume gray color image for internal methods

* chessboard: use std::swap

* chessboard: use Mat.dataend

* chessboard: fix compiler warnings

* chessboard: replace some checks witch CV_CHECK macro

* chessboard: fix comparison function for partial sort

* chessboard: small cleanup

* chessboard: use short license header

* chessboard: rename findChessboard2 to findChessboardSB

* chessboard: fix type in unit test

Support MSVC 2013 (#12486)

* Added CV_CONSTEXPR macro

* Utilize CV_NOEXCEPT and CV_CONSTEXPR

* Provides some Ptr<> logical operators

* added basic support for CV_16F (the new datatype etc.). CV_USRTYPE1 is now equal to CV_16F, which may break some [rarely used] functionality. We'll see

* fixed just introduced bug in norm; reverted errorneous changes in Torch importer (need to find a better solution)

* addressed some issues found during the PR review

* restored the patch to fix some perf test failures

* Fixed compilation error WITH_OPENMP under Windows

* Move up OpenMP condition

to share with opencv_contrib/xfeatures2d

* may be an typo fix

* remove identical branch,may be paste error

* add parentheses around macro parameter

* simplify if condition

* check malloc fail

* change the condition of branch removed by commit 3041502861318c85d901e8c08226ff67898c77ed

* simplify condition

* dims must > 0 or latter sz[dims-1] will underflow

* rewrote Mat::convertTo() and convertScaleAbs() to wide universal intrinsics; added always-available and SIMD-optimized FP16<=>FP32 conversion

* fixed compile warnings

* fix some more compile errors

* slightly relaxed accuracy threshold for int->float conversion (since we now do it using single-precision arithmetics, not double-precision)

* fixed compile errors on iOS, Android and in the baseline C++ version (intrin_cpp.hpp)

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds

* trying to fix ARM-neon builds