add type completer for 'topic pub' and 'service call'

[dirk-thomas]

Connect to #63. Fixes #63.

[mikaelarguedas]

code change looks good overall. Though it would be great to hide the --repeat option if only a single service type matches.
e.g.

$ ros2 service call /add_two_ints <TAB><TAB> 
example_interfaces/AddTwoInts  -r  --repeat

I'd expect this to just complete the matching service name

[dirk-thomas]

Though it would be great to hide the --repeat option if only a single service type matches.

I don't think that is technically possible (the results of one completer deciding to ignore the results of other completers). Anyway I wouldn't consider this within the scope of this PR.

[mikaelarguedas]

fair enough. Then maybe for another PR we can consider providing the same argument to ros2 topic pub ? Because it's a bit surprising from the user side to have a different behavior

[dirk-thomas]

Then maybe for another PR we can consider providing the same argument to ros2 topic pub ?

Sure, topic pub currently publishes with a fixed rate of once every second. A pull request to make this configurable would be great.

[mikaelarguedas]

code change looks good to me. I have one request on the docstrings before merging

[mikaelarguedas]

Nit: "an existing service type" I would recommend the documentation that it's returning the service type matching the passed service_name or all types (same for topics below)

[dirk-thomas]

That sounds good but exceeds the one line rule for the docblock 😉