When making a release export of a project, binaries built with the /MD flag do not work.
They are too slow and don't really test anything special.
- Uses matrix so that build steps don't need to be defined multiple times. - Caches godot-cpp bindings, so they only need to be built when the submodule version changes. - Uploads build artifacts for linux 32/64-bit, windows 64-bit and macOS 64-bit.
Closes #6
Closes #5