5.7.0

New features:

• Update to CodeMirror to 5.37, which includes f-string sytax for
  Python 3.6 (#3816)
• Update jquery-ui to 1.12 (#3836)
• Check Host header to more securely protect localhost deployments
  from DNS rebinding. This is a pre-emptive measure, not fixing a
  known vulnerability (#3766). Use .NotebookApp.allow_remote_access
  and .NotebookApp.local_hostnames to configure access.
• Allow access-control-allow-headers to be overridden (#3886)
• Allow configuring max_body_size and max_buffer_size (#3829)
• Allow configuring get_secure_cookie keyword-args (#3778)
• Respect nbconvert entrypoints as sources for exporters (#3879)
• Include translation sources in source distributions (#3925, #3931)
• Various improvements to documentation (#3799, #3800, #3806,
  #3883, #3908)

Fixing problems:

• Fix breadcrumb link when running with a base url (#3905)
• Fix possible type error when closing activity stream (#3907)
• Disable metadata editing for non-editable cells (#3744)
• Fix some styling and alignment of prompts caused by regressions in
  5.6.0.
• Enter causing page reload in shortcuts editor (#3871)
• Fix uploading to the same file twice (#3712)

See the 5.7 milestone on GitHub for a complete list of pull
requests involved in this release.