Add OpenCV parallel_for_ tutorial.

Use directly the doxygen snippet command for the Changing the contrast and brightness of an image tutorial. Extend the tutorial with a pratical example and with a gamma correction method to adjust the brightness of an image.

Modified the (R2,T2) computation documentation in the stereoCalibrate function documentation to display on two lines for clarity

Fix Documentation Typos (#7942)

Append zero to trailing decimal place for FileStorage JSON write of a float or double value (#7952)

* Fix for FileStorage JSON write of a float or double value that has no fractional part; appends a zero character after the trailing decimal place to meet JSON standard.

* strlen return to size_t type rather than unnecessary cast to int

Change `<=` to `<` to avoid accessing the first character of an empty string

3.2.0

* moved BLAS/LAPACK detection scripts from opencv_contrib/dnn to the main repository.

* trying to fix the bug with undefined symbols sgesdd_ and dgesdd_

* removed extra whitespaces; disabled LAPACK on IOS