Split up zeroing library BUILD rules

There was no good reason for one build rule to have both the interface
and a bunch of implementations; split it up and make the relevant users
depend on the libraries directly.

Change-Id: If6a0aa49dd7ea588b7325604658bc0594db4aac0
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/y2019/constants.h b/y2019/constants.h
index b6c1b55..a36e4b3 100644
--- a/y2019/constants.h
+++ b/y2019/constants.h
@@ -9,6 +9,8 @@
 #include "frc971/control_loops/drivetrain/camera.h"
 #include "frc971/control_loops/pose.h"
 #include "frc971/control_loops/static_zeroing_single_dof_profiled_subsystem.h"
+#include "frc971/zeroing/absolute_encoder.h"
+#include "frc971/zeroing/pot_and_absolute_encoder.h"
 #include "y2019/control_loops/drivetrain/drivetrain_dog_motor_plant.h"
 #include "y2019/control_loops/superstructure/elevator/elevator_plant.h"
 #include "y2019/control_loops/superstructure/intake/intake_plant.h"