Appveyor or Github CI

[chcg]

• github action as starting point (https://github.com/chcg/getboost/actions/runs/3256560986)
• add initial appveyor.yml CI config (https://ci.appveyor.com/project/chcg/getboost/builds/44506728)
• added dependabot action
• running from a CI job there is an issue with pushing the nuget packages as the apikey parameter is not available in that environment
• consider fixing:

WARNING: NU5125: The 'licenseUrl' element will be deprecated. Consider using the 'license' element instead. , see https://docs.microsoft.com/en-us/nuget/reference/nuspec#license <license type="expression">BSL-1.0</license> seems to be a replacement

@sergey-shandar Is that something you are interested in? Most likely the gh actions or the appveyor config could be extended to upload the resulting nuget packages to github and/or nuget package repo.

Should the readme be updated that the versions boost binaries used are not build on your own but taken from boost (e.g. https://archives.boost.io/release/1.88.0/binaries/) and build via https://github.com/teeks99/boost-release-windows.

[chcg]

@sergey-shandar Boost 1.78.0 is available. The needed changes to config.cs are already available here.