finish EBNF for topic and service names about design

[wjwwood]

@Theosakamg looks like I missed that one (foo/_/bar) when updating the rules. Thanks for pointing it out! I'll open a pr to fix it.

As for the current implementation, it doesn't follow this design doc yet (the implementation is lagging behind the document). We'll replace that line with something like this:

node_->get_name() + "/_get_parameters",

Or something similar, so that it uses the / namespace separator and is "hidden".

If you have further comments, please open a new issue or comment on the original pr (#90). This issue is specifically about completing the EBNF (candidate implementation is in #96).

[Theosakamg]

In design article it say :

must not have an underscore (_) followed by a forward slash (/), i.e. _/

https://github.com/ros2/design/blob/gh-pages/articles/115_topic_and_service_name_mapping.md#ros-2-topic-and-service-name-constraints

but in valid example :

foo/_/bar

https://github.com/ros2/design/blob/gh-pages/articles/115_topic_and_service_name_mapping.md#ros-2-name-examples

Can you clarify ?

[Theosakamg]

ind design acticle it say :

must not contain any number of repeated underscores (_)

https://github.com/ros2/design/blob/gh-pages/articles/115_topic_and_service_name_mapping.md#ros-2-topic-and-service-name-constraints

but in current implementation of Parameter service :
node_->get_name() + "__get_parameters",
https://github.com/ros2/rclcpp/blob/5894a9cd4eb0371e380dcbac73b74efae353fde2/rclcpp/src/rclcpp/parameter_service.cpp

It is excluded of Service name of parameter stack ?