4.0.0

Breaking changes

• kinto-wizard load now expects to find a buckets: root level in
  the YAML file. And kinto-wizard dump will now add it (fixes #59)

New feature

• Add a validate command to run JSON schema validation on the records
  locally. (fixes #61)

Internal changes

• To ease the transition between kinto-wizard 3 and kinto-wizard 4,
  handle both dump formats for a couple of releases. (#64)