Fix docs (#222)

* add missing documentation

* remove unnecessary visibility and warning macros

rcl/include/rcl/client.h

@@ -379,8 +379,7 @@ rcl_client_get_rmw_handle(const rcl_client_t * client);
 /**
  * The bool returned is `false` if client is invalid
  * The bool returned is `true` otherwise.
- * In the case where `false` is to be returned, an
+ * In the case where `false` is to be returned, an error message is set.
- * error message is set.
  * This function cannot fail.
  *
  * <hr>
@@ -392,6 +391,7 @@ rcl_client_get_rmw_handle(const rcl_client_t * client);
  * Lock-Free          | Yes
  *
  * \param[in] client pointer to the rcl client
+ * \param[in] error_msg_allocator a valid allocator or `NULL`
  * \return `true` if `client` is valid, otherwise `false`
  */
 RCL_PUBLIC

rcl/include/rcl/node.h

@@ -245,7 +245,7 @@ rcl_node_get_default_options(void);
  * <i>[1] if `atomic_is_lock_free()` returns true for `atomic_uint_least64_t`</i>
  *
  * \param[in] node rcl_node_t to be validated
- * \param[in] allocator a valid allocator or `NULL`
+ * \param[in] error_msg_allocator a valid allocator or `NULL`
  * \return `true` if the node and allocator are valid, otherwise `false`.
  */
 RCL_PUBLIC

rcl/include/rcl/publisher.h

@@ -354,6 +354,7 @@ rcl_publisher_get_rmw_handle(const rcl_publisher_t * publisher);
  * Lock-Free          | Yes
  *
  * \param[in] publisher pointer to the rcl publisher
+ * \param[in] error_msg_allocator a valid allocator or `NULL`
  * \return `true` if `publisher` is valid, otherwise `false`
  */
 RCL_PUBLIC

rcl/include/rcl/service.h

@@ -403,6 +403,7 @@ rcl_service_get_rmw_handle(const rcl_service_t * service);
  * Lock-Free          | Yes
  *
  * \param[in] service pointer to the rcl service
+ * \param[in] error_msg_allocator a valid allocator or `NULL`
  * \return `true` if `service` is valid, otherwise `false`
  */
 RCL_PUBLIC

rcl/include/rcl/subscription.h

@@ -358,6 +358,7 @@ rcl_subscription_get_rmw_handle(const rcl_subscription_t * subscription);
  * Lock-Free          | Yes
  *
  * \param[in] subscription pointer to the rcl subscription
+ * \param[in] error_msg_allocator a valid allocator or `NULL`
  * \return `true` if `subscription` is valid, otherwise `false`
  */
 RCL_PUBLIC

rcl/src/rcl/client.c

@@ -263,8 +263,6 @@ rcl_client_get_rmw_handle(const rcl_client_t * client)
   return client->impl->rmw_handle;
 }
 
-RCL_PUBLIC
-RCL_WARN_UNUSED
 rcl_ret_t
 rcl_send_request(const rcl_client_t * client, const void * ros_request, int64_t * sequence_number)
 {
@@ -286,8 +284,6 @@ rcl_send_request(const rcl_client_t * client, const void * ros_request, int64_t
   return RCL_RET_OK;
 }
 
-RCL_PUBLIC
-RCL_WARN_UNUSED
 rcl_ret_t
 rcl_take_response(
   const rcl_client_t * client,
@@ -318,7 +314,8 @@ rcl_take_response(
   return RCL_RET_OK;
 }
 
-bool rcl_client_is_valid(const rcl_client_t * client, rcl_allocator_t * error_msg_allocator)
+bool
+rcl_client_is_valid(const rcl_client_t * client, rcl_allocator_t * error_msg_allocator)
 {
   const rcl_client_options_t * options;
   rcl_allocator_t alloc =