* GAPI Fluid: SIMD for SubC kernel.

* Applied comments

* GAPI Fluid: SIMD for AddC kernel

* Final version

* Applied comments.

[G-API] Fixed Coverity issues

* Fixed Coverity issues
 - VectorRef&OpaqueRef m_kind = CV_UNKNOWN
 - added same-type overload for saturate()
 - sanitized resize value in ByteMemoryInStream::operator>> (std::string& str)
 - handled throws from ~GStreamingExecutor()

* Catching exception by const ref

* Addressing Sergey's comments

* Applied enable_if semanitcs to saturate(x, round) too

* Removed uncaught_exception, made destructor noexcept back

* Split Fluid ConvertTo to multiple functions to avoid ifs; added CV_ALWAYS_INLINE

* Added FIXME to address throwings from stop()

* Fix standalone

* Addressing comments

* Guarded SIMD optimizations properly

* Removed excess parameter from simd_impl functions

GAPI Fluid: SIMD Div kernel.

* HAL implementation for Div kernel

* Removed dbg lines

* Applied comments.

* Reworked

* Final version

Fluid: SIMD for Resize Linear 8UC3

* SIMD for fluid::Resize 8U3C

* Rework horizontal pass + add 8U4C case

* Reproduce stackoverflow test

* StackOverflow test

* SSE42 impl

* SSE42 impl improvement

* GAPI:SSE42 simd opt for Resize 8UC3. Final version

* Fix tests

* Conditional compilation fix

* Applied comments

* Applied comments. Step2

* Applied comments. Step2

GAPI: SIMD optimization for AbsDiffC kernel

* SIMD optimization for AbsDiffC kernel

* Applied comments

* Applying comments and refactoring: Remove new univ intrinsics.

* Performance experiment

* Applied comments.Step2

* Applied comments. Step3

GAPI: SIMD optimization for AddWeighted kernel.

* Add, sub, absdiff kernels optimization

* AddW kernel

* And, or kernels

* AddWeighted refactoring and SIMD opt for AbsDiffC kernel

* Remove simd opt of AbsDiffC kernel

* Refactoring

* Applied comments

* Refactoring.Step2

* Applied comments.Step2

Generic copy kernel

* Moved RMat wrapping of cv::Mats to StreamingInput

* Generalized GCopy kernel

* Generic GCopy kernel: applied review comments

Univ Intrinsics implementation of Add, Sub, Absdiff kernels

* Add, sub, absdiff kernels optimization

* avoid unused conditions

* add conditions for tail processing

[G-API]: Fluid: add mask, extend convertTo for CV_16S

* Add Fluid `mask` kernel + Acc. and Perf. tests
 - simple cycle implementation with restrictions on mask type and input/output type like in OCV/GPU kernels (mask - CV_8UC1 only, input/output - CV_8UC1, CV_16UC1, CV_16SC1)

* Added convertions from/to 16S

* `convertTo()` perf tests refactoring
 - add testing of `alpha` and `beta` parameters
 - fixed unreliable comparison
 - added instances to OCV, Fluid and GPU tests according to the changes

* Addressing comments
 - fixed multiple-channel mistake - prohibited multiple-channeling

* Reduced perf tests

[G-API]: Add Fluid bitwise operations implementation for (GMat, GScalar)

* Added Fluid `bitwise` with `Scalar` + acc.tests
 - simple loop implementation for Fluid used (no `hal`);
   - `Scalar` is casted to `int` in the beginning
 - tests just modified to work with `Scalar`
 - expected output in operators' tests fixed (operators can't change Mat's depth)
 - `float` `Scalar` `RNG` added, `RNG` reworked (`time` is used now), initialization of test fixtures reworked
   - if input or output is `float` Scalar is initialized by `float`
 - some problems with Fluid/OCV floating-point comparison difference stashed by `AbsSimilarPoints()` usage, FIXME added
 - divide-by-zero is now fixed differently and everywhere

* - Added perf_tests for bitwise_Scalar operations
 - due to errors of Fluid floating-point comparison operations, added support of different validation in Cmp perf_tests; added FIXME

 - reworked integral initialization of Scalar

* Addressing comments
 - NULL -> nullptr
 - Scalar convertion moved to the function
 - avoid -> avoiding

* Addressing comments

* CV_assert -> GAPI_assert

* Addressed DM comments
 - refactored convertScalarForBitwise()
 - removed unnecessary braces for switch

* Changed the operators tests
 - switch via `enum` implemented
 - infrastructure for that refactored

G-API: Unification of own:: structures with cv:: (Size, Point, Rect)

* deowned Size Rect Point

* Deownded Size Rect Point

* With Scalar

- addresses #15163: C++11 definition issue by @neheb

Changed quotes to brackets when including public includes (#14741)

* G-API: First steps with tutorial

* G-API Tutorial: First iteration

* G-API port of anisotropic image segmentation tutorial;
* Currently works via OpenCV only;
* Some new kernels have been required.

* G-API Tutorial: added chapters on execution code, inspection, and profiling

* G-API Tutorial: make Fluid kernel headers public

For some reason, these headers were not moved to the public
headers subtree during the initial development. Somehow it even
worked for the existing workloads.

* G-API Tutorial: Fix a couple of issues found during the work

* Introduced Phase & Sqrt kernels, OCV & Fluid versions
* Extended GKernelPackage to allow kernel removal & policies on include()

All the above stuff needs to be tested, tests will be added later

* G-API Tutorial: added chapter on running Fluid backend

* G-API Tutorial: fix a number of issues in the text

* G-API Tutorial - some final updates

- Fixed post-merge issues after Sobel kernel renaming;
- Simplified G-API code a little bit;
- Put a conclusion note in text.

* G-API Tutorial - fix build issues in test/perf targets

Public headers were refactored but tests suites were not updated in time

* G-API Tutorial: Added tests & reference docs on new kernels

* Phase
* Sqrt

* G-API Tutorial: added link to the tutorial from the main module doc

* G-API Tutorial: Added tests on new GKernelPackage functionality

* G-API Tutorial: Extended InRange tests to cover 32F

* G-API Tutorial: Misc fixes

* Avoid building examples when gapi module is not there
* Added a volatile API disclaimer to G-API root documentation page

* G-API Tutorial: Fix perf tests build issue

This change came from master where Fluid kernels are still used
incorrectly.

* G-API Tutorial: Fixed channels support in Sqrt/Phase fluid kernels

Extended tests to cover this case

* G-API Tutorial: Fix text problems found on team review

* Update G-API code base to 27-Sep-18

Changes mostly improve standalone build support

* G-API code base update 28-09-2018

* Windows/Documentation warnings should be fixed
* Fixed stability issues in Fluid backend
* Fixed precompiled headers issues in G-API source files

* G-API code base update 28-09-18 EOD

* Fixed several static analysis issues
* Fixed issues found when G-API is built in a standalone mode

* G-API Initial code upload

* Update G-API code base to Sep-24-2018

* The majority of OpenCV buildbot problems was addressed

* Update G-API code base to 24-Sep-18 EOD

* G-API code base update 25-Sep-2018

* Linux warnings should be resolved
* Documentation build should become green
* Number of Windows warnings should be reduced

* Update G-API code base to 25-Sep-18 EOD

* ARMv7 build issue should be resolved
* ADE is bumped to latest version and should fix Clang builds for macOS/iOS
* Remaining Windows warnings should be resolved
* New Linux32 / ARMv7 warnings should be resolved

* G-API code base update 25-Sep-2018-EOD2

* Final Windows warnings should be resolved now

* G-API code base update 26-Sep-2018

* Fixed issues with precompiled headers in module and its tests