CUDA implementation wants to convert std::vector<KeyPoint> <-> GpuMat.
There is no direct mapping from KeyPoint (mix of int/float fields)
into cv::Mat element type, so this conversion must be avoided.

Legacy mode is turned back for CUDA builds.

Remove unnecessary Non-ASCII characters from source code (#9075)

* Remove unnecessary Non-ASCII characters from source code

Remove unnecessary Non-ASCII characters and replace them with ASCII
characters

* Remove dashes in the @param statement

Remove dashes and place single space in the @param statement to keep
coding style

* misc: more fixes for non-ASCII symbols

* misc: fix non-ASCII symbol in CMake file

Fix #8177

In the previous version only the default stream was/could be used, i.e.
cv::cuda::Stream::Null().

With this change, HOG::compute() will now run in parallel over different
cuda::Streams.

The code has been reordered so that all data allocation is completed
first, then all the kernels are run in parallel over streams.

Fix #8177

See https://github.com/Itseez/opencv/issues/5721

COMMENTS:
* The second __syncthreads() is necessary, I am sure of that.
* The code works without the first __syncthreads() too, but I have however added it for symmetry. Anyway it doesn't affect time performances, I have checked it with some profiling with nvvp

changed hog to work with variable parameters and changed the hog sample to test it with more options

added comments and tests

use abstract interface with hidden implementation

move GPU constants initialization from constructor to compute method