Syntax highlighting for ROS (Robot Operating System) files.

Provides `ros-face-msg-mode', a major mode with syntax
highlighting for ROS interface definition files:

- `.msg' - message definitions
- `.srv' - service definitions
- `.action' - action definitions

Provides `ros-face-idl-mode', a major mode with syntax
highlighting for ROS 2 IDL interface files (`.idl').

Also registers `.launch' files to open in `nxml-mode'.