message: doc(c-api) Mark some types as unstable.
diff: use super::super::engine::wasm_config_t;
  use super::target_lexicon::wasm_target_t;
  -/// Updates the configuration to specify a particular target for the engine.
  +/// Unstable non-standard Wasmer-specific API to update the
  +/// configuration to specify a particular target for the engine.
  ///
  /// # Example
  ///
  