Add declination, enu, um6, upstart to doc generation

enu— already in groovy docs, just adding to hydro
um6— a rewritten driver for the CHRobotics UM6
declination— provides a simple node which computes compass magnetic declination from a NavSatFix and can then transform an IMU message accordingly.
robot_upstart— tools for launching ROS from upstart.

(For others tuning in, [discussion on upstart name here](https://github.com/clearpathrobotics/upstart/issues/1).)