fix(event): Chase etcd index on EcodeEventIndexCleared
refactor(registry): Use a single watcher in EventStream
refactor(registry): Check for path prefix in event filters
Merge pull request #411 from bcwaldon/chase-that-index

Chase that index
fix(registry): lazily migrate legacy payloads
Merge pull request #413 from bcwaldon/lazy-migrate

fix(registry): lazily migrate legacy payloads
refactor(registry): move fleetctl's Registry interface to registry proper
Merge pull request #323 from jonboulle/323

refactor(registry): improve registry interface and obviate fleetctl's special one
feat(registry): abstract out storage backend for Registry

This is something of a proof-of-concept/WIP draft.

Following on from the creation of the Registry interface, this creates a
Storage interface to encapsulate where Registries actually store their
data. The intention is to allow proper testing of the main fleet registry's
code (including serializing/deserializing, etc) and reduce the coupling
of the Registry with etcd.

This change adds an example MemoryStorage template (which requires
further implementation to facilitate tests which are actually useful)