v0.2.0

The first release with a transaction handle, and the first that a
consuming application can depend on without a local replace.

v0.1.0 predates db.go entirely: sqlb.DB and sqlb.New — the handle every
data layer takes — landed after it, along with array columns, codegen
type overrides, a JSON filter tree, schema-impact diffing, and a fix for
an expansion carrying its target's scope onto the join.

Cut for the studio-apps port, which could not compile against v0.1.0.