2.10.0

Protocol

• Moved userid attribute to a dedicated user mapping in the hello
  view.
• Fixed 503 error message to mention backend errors in addition to unavailability.
• Set cache headers only when anonymous (fixes #449)
• Follow redirections in batch subrequests (fixes #511)
• When recreating a record that was previously deleted, status code is now 201
  (ref #530).

New features

• Follow redirections in batch subrequests (fixes #511)
• Add a readonly setting to run the service in read-only mode. (#525)
• If no client cache is set, add Cache-Control: no-cache by default,
  so that clients are forced to revalidate their cache against the server
  (#522, ref Kinto/kinto#231)

Bug fixes

• Fix PostgreSQL error when deleting an empty collection in a protected
  resource (fixes #528)
• Fix PUT not using create() method in storage backend when tombstone exists
  (fixes #530)
• Delete tombstone when record is re-created (fixes #518)
• Fix crash with empty body for PATCH (fixes #477, fixes #516)
• Fix english typo in 404 error message (fixes #527)

Internal changes

• Better pycache cleaning