control-systems

While converting the developer docs docuemnt to markdown I stumbled
upon the envvar directive. I think it would be nice to use that generally,
but it needs some work. For one all variables from environment.rst show
up as second level TOC entries in the main navigation now. Which is something
we do not want. The developer docs should also use the referencing mechanism
and maybe we want to add a

class_name is the nomenclature of pluginlib which in this case doesn't really help people understand what this is supposed to be. We already use plugin_name elsewhere to refer to the same thing, let's rename this field in hardware_interface_info

Originally posted by @destogl in ros-controls/ros2_control#589 (comment)

Current docstring contents are not sufficient. Every function, regardless of trivialness, require at least one usage example.