message: reactor.Scheduler: avoid std::bind
  And use run_later rather than duplicating it.
diff: @@ -552,25 +552,17 @@ namespace elle
  new Thread(*this, name, f, true);
  }
  - namespace
  - {
  - void
  - _call_later_helper(Scheduler* sched,
  - std::function<void ()> const& f,
  - Duration delay)
  - {
  - sched->current()->sleep(delay);
  - f();
  - }
  - }
  -
  void
  Scheduler::call_later(std::string const& name,
  std::function<void ()> const& f,
  Duration delay)
  {
  - new Thread(*this, name,
  - std::bind(&_call_later_helper, this, f, delay), true);
  + run_later(name,
  + [this, f, delay]
  + {
  + this->current()->sleep(delay);
  + f();
  + });
  }
  /*----------------.
  @@ -641,13 +633,12 @@ namespace elle
  {
  if (error == boost::asio::error::operation_aborted)
  return;
  - new reactor::Thread(sched, "signal handler", handler, true);
  - set.async_wait(std::bind(&signal_callback,
  - std::ref(sched),
  - std::ref(set),
  - handler,
  - std::placeholders::_1,
  - std::placeholders::_2));
  + sched.run_later("signal handler", handler);
  + set.async_wait([&sched, &set, handler]
  + (boost::system::error_code const& error, int dummy)
  + {
  + signal_callback(sched, set, handler, error, dummy);
  + });
  }
  std::string signal_string(int const signal)
  @@ -667,12 +658,11 @@ namespace elle
  ELLE_TRACE_SCOPE("%s: handle signal %s", *this, signal_string(signal));
  auto set = std::make_unique<boost::asio::signal_set>(this->io_service(),
  signal);
  - set->async_wait(std::bind(&signal_callback,
  - std::ref(*this),
  - std::ref(*set),
  - handler,
  - std::placeholders::_1,
  - std::placeholders::_2));
  + set->async_wait([this, &set=*set, handler]
  + (boost::system::error_code const& error, int dummy)
  + {
  + signal_callback(*this, set, handler, error, dummy);
  + });
  this->_signal_handlers.emplace_back(std::move(set));
  }
  