message: Enable streaming of all announced types
diff: #include <unordered_map>
  #include "caf/fwd.hpp"
  +#include "caf/stream.hpp"
  #include "caf/config_value.hpp"
  #include "caf/config_option.hpp"
  #include "caf/actor_factory.hpp"
  @@ -163,11 +164,21 @@ public:
  || (std::is_default_constructible<T>::value
  && std::is_copy_constructible<T>::value),
  "T must provide default and copy constructors");
  + using stream_type = stream<T>;
  + std::string stream_name = "stream<";
  + stream_name += name;
  + stream_name += ">";
  static_assert(detail::is_serializable<T>::value, "T must be serializable");
  type_names_by_rtti.emplace(std::type_index(typeid(T)), name);
  value_factories_by_name.emplace(std::move(name), &make_type_erased_value<T>);
  value_factories_by_rtti.emplace(std::type_index(typeid(T)),
  &make_type_erased_value<T>);
  + type_names_by_rtti.emplace(std::type_index(typeid(stream_type)),
  + stream_name);
  + value_factories_by_name.emplace(std::move(stream_name),
  + &make_type_erased_value<stream_type>);
  + value_factories_by_rtti.emplace(std::type_index(typeid(stream_type)),
  + &make_type_erased_value<stream_type>);
  return *this;
  }
  