Add feedforward components (#2045)

Add helper classes for computing feedforwards with parameters supplied by the characterization tool.

wpiutil/src/main/native/include/wpi/MathExtras.h

@@ -838,6 +838,12 @@ SaturatingMultiplyAdd(T X, T Y, T A, bool *ResultOverflowed = nullptr) {
   return SaturatingAdd(A, Product, &Overflowed);
 }
 
+// Typesafe implementation of the signum function.  Returns -1 if negative, 1 if positive, 0 if 0.
+template <typename T>
+int sgn(T val) {
+  return (T(0) < val) - (val < T(0));
+}
+
 } // namespace wpi
 
 #endif