Template Spline with the number of control points.

It's just about as hard to go from 4 to 6 as 4 to N...  Parker provided
me with the algorithm.

Change-Id: I8bc665b8798d4c31a58c17fa9f67fcf7b601b987
diff --git a/frc971/control_loops/drivetrain/BUILD b/frc971/control_loops/drivetrain/BUILD
index ac6e2d3..9bb335c 100644
--- a/frc971/control_loops/drivetrain/BUILD
+++ b/frc971/control_loops/drivetrain/BUILD
@@ -263,6 +263,7 @@
     srcs = ["spline.cc"],
     hdrs = ["spline.h"],
     deps = [
+        "//frc971/control_loops:binomial",
         "//third_party/eigen",
     ],
 )