When go test fails, we would not kill any extra node processes lying
around. In AppVeyor, not killing these causes the job to hang until we
reach the AppVeyor timeout. Explicitly killing the jobs ensures
AppVeyor ends quickly.
We use `git describe --tags` to construct a version number based on
the current version tag.
The properties VERSION (when using make) and Version (when using
MSBuild) can be explicitly set to use a fixed value instead.
Fixes#13
Now that we no longer recursively call yarn via yarn run and scripts,
we can use a `--mutex network` directive in a .yarnrc file at the root
of the repository to prevent multiple copies of yarn running
concurrently.
