Wrap documentation examples in code blocks (#830)

This makes the code examples easier to read in the generated documentation.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

rclcpp/include/rclcpp/node.hpp

@@ -151,6 +151,7 @@ public:
    *
    * For example, all of these cases will work:
    *
+   * ```cpp
    * pub = node->create_publisher<MsgT>("chatter", 10);  // implicitly KeepLast
    * pub = node->create_publisher<MsgT>("chatter", QoS(10));  // implicitly KeepLast
    * pub = node->create_publisher<MsgT>("chatter", QoS(KeepLast(10)));
@@ -160,6 +161,7 @@ public:
    *   rclcpp::QoS custom_qos(KeepLast(10), rmw_qos_profile_sensor_data);
    *   pub = node->create_publisher<MsgT>("chatter", custom_qos);
    * }
+   * ```
    *
    * The publisher options may optionally be passed as the third argument for
    * any of the above cases.
@@ -904,6 +906,7 @@ public:
    *
    * For an example callback:
    *
+   * ```cpp
    * rcl_interfaces::msg::SetParametersResult
    * my_callback(const std::vector<rclcpp::Parameter> & parameters)
    * {
@@ -917,6 +920,7 @@ public:
    *   }
    *   return result;
    * }
+   * ```
    *
    * You can see that the SetParametersResult is a boolean flag for success
    * and an optional reason that can be used in error reporting when it fails.
@@ -1127,6 +1131,7 @@ public:
    *
    * For example, consider:
    *
+   * ```cpp
    * auto node = std::make_shared<rclcpp::Node>("my_node", "my_ns");
    * node->get_sub_namespace();  // -> ""
    * auto sub_node1 = node->create_sub_node("a");
@@ -1136,6 +1141,7 @@ public:
    * auto sub_node3 = node->create_sub_node("foo");
    * sub_node3->get_sub_namespace();  // -> "foo"
    * node->get_sub_namespace();  // -> ""
+   * ```
    *
    * get_namespace() will return the original node namespace, and will not
    * include the sub-namespace if one exists.
@@ -1157,6 +1163,7 @@ public:
    *
    * For example, consider:
    *
+   * ```cpp
    * auto node = std::make_shared<rclcpp::Node>("my_node", "my_ns");
    * node->get_effective_namespace();  // -> "/my_ns"
    * auto sub_node1 = node->create_sub_node("a");
@@ -1166,6 +1173,7 @@ public:
    * auto sub_node3 = node->create_sub_node("foo");
    * sub_node3->get_effective_namespace();  // -> "/my_ns/foo"
    * node->get_effective_namespace();  // -> "/my_ns"
+   * ```
    *
    * \sa get_namespace()
    * \sa get_sub_namespace()

rclcpp/include/rclcpp/parameter_events_filter.hpp

@@ -47,12 +47,16 @@ public:
    *    EventType NEW, DELETED, or CHANGED
    *
    * Example Usage:
+   *
    * If you have recieved a parameter event and are only interested in parameters foo and
    * bar being added or changed but don't care about deletion.
+   *
+   * ```cpp
    * auto res = rclcpp::ParameterEventsFilter(
    *   event_shared_ptr,
    *   {"foo", "bar"},
    *   {rclcpp::ParameterEventsFilter::EventType::NEW, rclcpp::ParameterEventsFilter::EventType::CHANGED});
+   * ```
    */
   RCLCPP_PUBLIC
   ParameterEventsFilter(

rclcpp/include/rclcpp/waitable.hpp

@@ -128,7 +128,7 @@ public:
    *
    * Example usage:
    *
-   * ```
+   * ```cpp
    * // ... create a wait set and a Waitable
    * // Add the Waitable to the wait set
    * bool add_ret = waitable.add_to_wait_set(wait_set);