QoS - API and implementation for Liveliness and Deadline event callbacks

[minggangw]

No description provided.

[minggangw]

Continued from #498

for this thing I need to add one more paramter in the methods which is used for creating Publisher/Subsciber, so I m asking if need to embed this new parameter inside options object or add just add a new paramter field.
What guidelines is followed I dont know

We suggest aligning with interfaces of rclpy, there is no guideline for designing an interface

what is the use of timerCallback(),I have seen that at the end this function calls rcl_timer.c but cant understand what is its role

timer.callback() will trigger the callback function passed when creating this timer

[caelinsutch]

Is this taken?

[minggangw]

No, it' not. Please feel free to take it if you are interested in.