Use github actions for CI about hunter

[bkotzz]

Agreed, we’ve been investigating GitHub actions and it looks good for our needs. We’ve signed up for the beta in this repo so we have the ability to start using it. Feel free to make some progress on this and put up PRs

[cristianadam]

I've mentioned on gitter, but I thought I should mention it here too:

I've blogged about how to add GitHub Actions to a C++ project using CMake: https://cristianadam.eu/20191222/using-github-actions-with-c-plus-plus-and-cmake/

[cristianadam]

I have a followup to the GitHub Actions blog article, https://cristianadam.eu/20200113/speeding-up-c-plus-plus-github-actions-using-ccache/

Using ccache speeds up things considerably.

[rbsheth]

Done with #250