Add images used in the ROS wiki doc.
Add basic description in package.xml.
Rename hold_trajectory_duration

- hold_trajectory_duration -> stop_trajectory_duration for more clarity.

- During Hydro, hold_trajectory_duration will still work, giving a deprecation
  warning.
Merge branch 'hydro-devel' of https://github.com/willowgarage/ros_controllers into hydro-devel
Update README.md

Factor out user documentation to the ROS wiki.
Image update.
Add self as ros_controllers maintainer.
Merge branch 'hydro-devel' of https://github.com/willowgarage/ros_controllers into hydro-devel
Added new has_velocity flag that indiciates if a target velocity has been set
Merge pull request #54 from davetcoleman/effort_position_controller_fix

Added new has_velocity flag that indiciates if a target velocity has been set