Add support for GitHub Actions

[Croydon]

Changelog: Feature: Add support for GitHub Actions

Fixes #474

[uilianries]

That's great! Thanks a lot @Croydon

[annulen]

Could you suggest any Conan recipe repository with multiplatform (i.e. different compilers, operating systems) build matrix which could be used as a template?

[Croydon]

At Bincrafters we use GitHub Actions only for Linux so far

You can see our template at https://github.com/bincrafters/templates/blob/32ab0bae69c58c3c842e4aba502687d9e9ccaebf/default/.github/workflows/conan.yml#L1

And see an example e.g. at https://github.com/bincrafters/conan-qt/actions or https://github.com/bincrafters/conan-cairo/actions

[annulen]

Thanks! msvc.yml and mingw.yml from Qt are particularly useful. My main use cases are:

• Replace AppVeyor for building MSVC and MinGW packages - GitHub Actions provides 20 concurrent builds for free, while AppVeyor only one, which makes building large packages like ICU quite painful. There is no image with VS2015, though I guess it should be possible to install it via chocolatey
• Build new recipe for Windows, Linux, and macOS and have all builds and configurations in the same place

[Croydon]

There is no image with VS2015, though I guess it should be possible to install it via chocolatey

Regarding this, please consider upvoting actions/runner-images#387

Installing VS2015 on the fly takes way too long