message: Document CAF 0.17.5 additions
diff: @@ -147,6 +147,24 @@ is based on [Keep a Changelog](https://keepachangelog.com).
  ## [0.17.5] - Unreleased
  +### Added
  +
  +- In order to allow users to start migrating towards upcoming API changes, CAF
  + 0.17.5 includes a subset of the CAF 0.18 `type_id` API. Listing all
  + user-defined types between `CAF_BEGIN_TYPE_ID_BLOCK` and
  + `CAF_END_TYPE_ID_BLOCK` assigns ascending type IDs. Only one syntax for
  + `CAF_ADD_ATOM` exists, since the atom text is still mandatory. Assigning type
  + IDs has no immediate effect by default. However, the new function
  + `actor_system_config::add_message_types` accepts an ID block and adds
  + runtime-type information for all types in the block.
  +- In order to opt into the compile-time checks for all message types, users can
  + set the `CAF_ENABLE_TYPE_ID_CHECKS` CMake flag to `ON` (pass
  + `--enable-type-id-checks` when using the `configure` script). Building CAF
  + with this option causes compiler errors when sending a type without a type ID.
  + This option in conjunction with the new `add_message_types` function removes a
  + common source of bugs: forgetting to call `add_message_type<T>` for all types
  + that can cross the wire.
  +
  ### Changed
  - Our manual now uses `reStructuredText` instead of `LaTeX` (backport from
  