Perform basic turret auto-aiming

Implements a basic aimer which will shoot balls straight at the origin.

This still leaves a variety of things to be done:
-Actually shooting at the correct coordinates.
-Choosing between whether to shoot at the 2-point goal or 3-point goal.
-Managing turret wrap/redundancy intelligently.
-Shooting on the fly.

Change-Id: If4fc6249951faa5300411a0ca7d29da9e11dbb15
diff --git a/y2020/control_loops/superstructure/superstructure_status.fbs b/y2020/control_loops/superstructure/superstructure_status.fbs
index e8f7637..61208da 100644
--- a/y2020/control_loops/superstructure/superstructure_status.fbs
+++ b/y2020/control_loops/superstructure/superstructure_status.fbs
@@ -26,6 +26,13 @@
   accelerator_right:FlywheelControllerStatus;
 }
 
+table AimerStatus {
+  // The current goal angle for the turret auto-tracking, in radians.
+  turret_position:double;
+  // The current goal velocity for the turret, in radians / sec.
+  turret_velocity:double;
+}
+
 table Status {
   // All subsystems know their location.
   zeroed:bool;
@@ -43,6 +50,9 @@
 
   // Status of the control_panel
   control_panel:frc971.control_loops.RelativeEncoderProfiledJointStatus;
+
+  // Status of the vision auto-tracking.
+  aimer:AimerStatus;
 }
 
 root_type Status;