message: elle.exception_string(): Inline fetching of current_exception().
  Avoids having to somehow import reactor's cxa_get_globals() into
  libelle_core when those are two separate dlls.
diff: @@ -15,7 +15,13 @@ namespace elle
  class WeakBuffer;
  std::string
  - exception_string(std::exception_ptr err = std::exception_ptr{});
  + exception_string(std::exception_ptr err);
  + inline
  + std::string
  + exception_string()
  + {
  + return exception_string(std::current_exception());
  + }
  }
  // Keep after the previous fwd decls.
  