Create Python wrapper for distance_spline.

Also reformatted libspline.py
Also made the constructor for Spline more useful.

Change-Id: I0e54a54df7c872ba0c06f9d6ad414d2880c157d7
diff --git a/frc971/control_loops/python/BUILD b/frc971/control_loops/python/BUILD
index bedd763..8d467e1 100644
--- a/frc971/control_loops/python/BUILD
+++ b/frc971/control_loops/python/BUILD
@@ -82,10 +82,20 @@
         "libspline.py",
     ],
     data = [
-        "//frc971/control_loops/drivetrain:spline.so"
+        "//frc971/control_loops/drivetrain:spline.so",
     ],
 )
 
+py_test(
+    name = "lib_spline_test",
+    srcs = [
+        "lib_spline_test.py",
+    ],
+    deps = [
+        ":libspline",
+    ]
+)
+
 py_library(
     name = "polydrivetrain",
     srcs = [