Changes from pull request #139.
Tested in noetic. Just clone a build.
Launch file example:
<node name="robot_state_publisher2" pkg="robot_state_publisher2" type="robot_state_publisher2" ns="$(arg ns)">
<param name="prefix_tf_with" value="$(arg ns)"/>
<param name="robot_description" value="/$(arg ns)/robot_description"/>
</node>