4.0.1

Bug fixes

• Return 400 error response when history is filtered with unknown field
• Fix crash on permissions endpoint when history is enabled (#774)
• Fix crash on history when interacting via the bucket plural endpoint (/buckets) (fixes #773)

Internal changes

• Fix documentation of errors codes (fixes #766)
• kinto.id_generator was removed from documentation since it does not
  behave as expected (fixes #757, thanks @doplumi)
  folder and a kinto.core.testing module was introduced for tests helpers
  (fixes #605)
• In documentation, link the notion of principals to the permissions page instead
  of glossary
• Add details about PATCH behaviour (fixes #566)