Knative Build release v0.3.0

Meta

More regular releases

0.3 is the first release of our new schedule of releasing every 6 weeks.
This release is a smaller delta than 0.2 because of this shorter development
cycle.

Transitioning to Pipelines

Since 0.2, most new development work has focused on the
Pipeline repo.

Kubernetes 1.11 is now required

We now use the Kubernetes /status sub-resource support, which went Beta in K8s
1.11.

Features

Multiple Input Sources

The Build spec can now specify either a single source or multiple sources.
If multiple sources are requested, each will be fetched in order and placed into
a directory under /workspace named after the source's name field. (#392)

Other Features

A Build's annotations are copied to the underlying Pod. (#469)

A Build's status is updated to indicate validation errors (#471)

The Build controller is subject to a PodSecurityPolicy which limits what it
can do and enables cluster operators to specify further limiting policies.
(#509)