Provides a global controller cache.

Controllers ensure that blocking tailers will unblock when an
appender writes to a blocking queue. Each queue has one and only one
corresponding controller. Once a controller has been bound to a
queue on disk, it should never be removed for the lifetime of the
app, unless the queue has been deleted on disk, in which case, the
controller must be purged from the cache.

Extends com.stuartsierra.dependency for disconnected graphs.

Core Cues API.

Provides Cues test fixtures.