Xacro porting to ROS2

Hi,

@codebot and @rhaschke

As @prasenjitdan has mentioned our interest in porting xacro package to ROS2,
We have started porting xacro code and test cases as per ROS2 guidelines to support ROS2 bouncy.
We want to share this development but there is no ROS2 development branch on https://github.com/ros/xacro/branches.
I have created github ticket to create ros2-devel branch. https://github.com/ros/xacro/issues/196

Can anybody create ros2-devel branch so that we can raise PR against it.

Thanks,
Vandana