ROS2 uses catkin for the build

[jediofgever]

Hi,
I realize catkin is being used to build the ROS2 branch.
Should not ament be used instead,
I did some quick replacement and could build package with colon build. https://github.com/jediofgever/serial/tree/ros2

if there is no particular reason for the use of catkin I might be able to open a PR.

Regards.