Substitution-Superpowers

Make it easy to generate property-sets by merging structured files together, and
make said context available to a handlebars powered engine to perform substitutions.

This allows to bring together context owned by various entities into a single aggregated
one, with the possibility for later contexts to override earlier ones.

With this capability, it's also possible to substitute secrets into files, for example
like this: sy sub base.json sub/ours.yaml <(sy vault show secret.yaml) < deployment.yml | kubectl apply -f -.

Read more in the documentation.