Moved decel_at_current to bottom
Add continuous_strafe function, and more comments
Removed odo callback from vfh_server.

It was duplicating the odo callback in the simple_motion object.
Now it just gets the robot position from it.
Deleted all references to self._robot_pose
Removed current_error from simple_motion.

This didn't make a lot of sense.  Error should be produced by the
server that is using the simple_motion object.   The meaning of error
is different for the different servers.
vfh_move server now stops the simple_motion object

Now stop slows down at acceleration by default.   If you want to
stop at stop_deceleration, call estop()