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/frc971/zeroing/continuous_absolute_encoder.h b/frc971/zeroing/continuous_absolute_encoder.h
index b912e84..e11d866 100644
--- a/frc971/zeroing/continuous_absolute_encoder.h
+++ b/frc971/zeroing/continuous_absolute_encoder.h
@@ -5,6 +5,7 @@
 
 #include "flatbuffers/flatbuffers.h"
 
+#include "aos/containers/error_list.h"
 #include "frc971/zeroing/zeroing.h"
 
 namespace frc971 {