Add build cache

[leafo]

Store the results to the builds to github releases, then use those binaries when installing to skip compiling lua.

[leafo]

I added a publish workflow for new tags: https://github.com/leafo/gh-actions-lua/blob/master/.github/workflows/publish.yml

[leafo]

release zips are now available here: https://github.com/leafo/gh-actions-lua/releases

It should be as simple as downloading and extracting them to install lua

[leafo]

Implemented with #17