Previously, we would push all tagged releases into the stable component,
including alphas and rc's. Let's use some regex to only push stable
releases which conform to tag "^v+\d\.+\d\.+\d$"
so we ONLY get the manually published releases into the stable
component.
All pre-releases go into the "unstable" component for now. Nightly builds
go into the "dev" component (as before) and feature branches still get
their dedicated component named after the branch.
TODO: It would be nifty if stable releases would ALSO be published at the
unstable component.
