Implement windows runner for Github Actions

[Razdeep]

Currently, Github Actions for Linux and Mac works.
Add windows runner in ./github/workflows/cmake.yml

[cindy-luck]

Currently, Github Actions for Linux and Mac works.
Add windows runner in ./github/workflows/cmake.yml

hello, this is my first time trying out open source project. Will be appreciated if you could give some hints.
I was trying to add under matrix.configuration with

• {
  os: windows-latest,
  install_dependencies_command: "python -m pip install --upgrade pip && pip install opencv-python",
  cmake_configure_command: "cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE",
  }

[Razdeep]

This issue is actually dependent on issue #1 . I would recommend you to try building and testing in windows first.
Maybe you can start with writing a little documentation on how to build on windows.
Currently, splitwebp works seamlessly on Linux and MacOS.