• Added FAQ entry about crashes when loading more than one
  C++ library that statically links libstdc++ (gh#393)
  
• Fixed test suite failures under a hardened-runtime Perl (such as
  Apple's system Perl on macOS) where dlopen refuses a relative
  path, by resolving the test library path to an absolute path
  (gh#409)
  
• Closures called from a thread that was not created by Perl
  (for example a thread created by the C library) now abort with
  a diagnostic pointing to the FAQ instead of crashing or silently
  using the interpreter from two threads at once. Added a FAQ
  entry describing this limitation and the usual workaround
  (gh#399, gh#416)
  
• Fixed double free during global destruction when a Perl thread
  is created while a closure exists, since the closure's C data
  was being cloned into the child thread (gh#416)