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This patch implements the basic framework of the ros2brige, which adopt
the rosbridge v2.0 protocol
(https://github.com/RobotWebTools/rosbridge_suite/blob/develop/ROSBRIDGE_PROTOCOL.md),
so this bridge designed for ROS2 is compatible with the current
roslibjs library.

Currently all the ROS operations(op) are supported, you can create a
publisher/subscription/client/service, and there are examples already.
To try the examples, please run:
node index.js
node examples/index.js

Then open the browser, input the URL like:
http://localhost:3000/html/client.html

One known issue is that when the websocket connection is closed, the resources will
not get released which leads an error.