[Webthing-CPP] add new port

[bw-hro]

Webthing-CPP is a modern CPP/C++17 implementation of the WebThings API.

• [x] Changes comply with the maintainer guide.
• [x] The name of the port matches an existing name for this component on https://repology.org/ if possible, and/or is strongly associated with that component on search engines.
• [x] Optional dependencies are resolved in exactly one way. For example, if the component is built with CMake, all find_package calls are REQUIRED, are satisfied by vcpkg.json's declared dependencies, or disabled with CMAKE_DISABLE_FIND_PACKAGE_Xxx.
• [x] The versioning scheme in vcpkg.json matches what upstream says.
• [x] The license declaration in vcpkg.json matches what upstream says.
• [x] The installed as the "copyright" file matches what upstream says.
• [x] The source code of the component installed comes from an authoritative source.
• [x] The generated "usage text" is accurate. See adding-usage for context.
• [x] The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• [x] Only one version is in the new port's versions file.
• [x] Only one version is added to each modified port's versions file.

[Cheney-W]

Webthing-CPP is a header-only repository, so please refer to the contents of the following files to modify the files of Webthing-CPP: https://github.com/microsoft/vcpkg/blob/master/ports/cimg/vcpkg.json https://github.com/microsoft/vcpkg/blob/master/ports/cimg/portfile.cmake

[bw-hro]

Hi, Cheney thank you very much for your support. All tests now appear to have been completed and passed. Is anything else missing?

[Cheney-W]

Usage test passed with x64-windows triplet.

[Cheney-W]

There is nothing else. I think this pr just needs to wait to be merged.