macOS driver script to build for all Python versions

The driver script needs to

1. Create the virtualenv's for Python 3.5, 3.6, 3.7
2. Install scikit-build into the virtualenv's
3. Run the build for each virtualenv

Find the macOS driver script in the repository and read how it currently creates environments and starts builds. Run the existing script first, then verify that separate environments for Python 3.5, 3.6, and 3.7 install scikit-build and each completes the build. Done means all three builds run successfully on macOS.

Vom Indexierungsmodell aus dem Issue-Text verfasst.