Pot + absolute encoder zeroing class

This class takes a pot, absolute encoder, and relative encoder and uses
them to compute the offset.  It doesn't yet detect errors or wait until
stopped.

Change-Id: I74bc2031132974d9f3e2e6ddf93b954384a6ce2c
diff --git a/frc971/zeroing/BUILD b/frc971/zeroing/BUILD
index 0b8799f..4b3745f 100644
--- a/frc971/zeroing/BUILD
+++ b/frc971/zeroing/BUILD
@@ -36,6 +36,7 @@
     'zeroing.h',
   ],
   deps = [
+    ':wrap',
     '//frc971/control_loops:queues',
     '//frc971:constants',
   ],