Make sundry improvements/bug fixes to auto-aiming

This includes:
-Adding some velocity and voltage limits to prevent excessive
 velocity and acceleration.
-Logging more information in the status message.
-Fixing calculation of the desired turret velocity.

Change-Id: I83840bc1db9dda003be63e594d826fc97fa509e8
diff --git a/y2020/control_loops/superstructure/superstructure_status.fbs b/y2020/control_loops/superstructure/superstructure_status.fbs
index 81293d3..dc6116c 100644
--- a/y2020/control_loops/superstructure/superstructure_status.fbs
+++ b/y2020/control_loops/superstructure/superstructure_status.fbs
@@ -36,6 +36,11 @@
   turret_velocity:double;
   // Whether we are currently aiming for the inner port.
   aiming_for_inner_port:bool;
+  // The current distance to the target, in meters.
+  target_distance:double;
+  // The current "shot distance." When shooting on the fly, this may be
+  // different from the static distance to the target.
+  shot_distance:double;
 }
 
 table Status {