Merge ocl and/or/xor operators into one kernel each.
Add contributing page for Github
Eliminate the need of ::testsing::ValuesIn() for CV_ENUM

Also cv::, cv::gpu:: and cv::ocl:: namespace prefixes can be safely omitted
inside CV_ENUM and CV_FLAGS
Merge pull request #821 from taka-no-me:contributing
Let wave_size=1 on CPU.
Add clamping for y dimension.
Merge pull request #822 from taka-no-me:better_cv_enum
Merge pull request #825 from pengx17:2.4_query_cpu_wavesize
Merge pull request #826 from pengx17:2.4_canny_clampfix
Redo the Sphinx check to do the same thing on all platforms.

This also fixes the bug where the Sphinx version gets detected as
"Sphinx vX.Y.Z" instead of "X.Y.Z" on Unix-like systems.
Merge pull request #817 from pengx17:2.4_ocl_bitwise_cleanup
Merge pull request #829 from SpecLad:sphinx-ver-1