v6.4.0

Enhancements

• FeatureFlags are now a copy-on-write structure, and so don't need to be defensive copied on a crashing thread
  #2005
• The default redactedKeys in ObjectJsonStreamer is now static and shared, reducing the overhead of some leaveBreadcrumb calls (those with complex metadata)
  #2008
• Allow Bugsnag.startSession to be called with automatic session tracking, and not have the first manual session be over written by the first automatic session.
  #2006

Bug fixes

• Refreshing the NDK symbol table is now protected by a soft-lock to avoid possible double-free conditions
  #2007