Add default values for b and zeta in RamseteController (#2145)

Values b=2.0 and zeta=0.7 have been well-tested to produce desirable results.

wpilibc/src/main/native/include/frc/controller/RamseteController.h

@@ -54,6 +54,13 @@ class RamseteController {
    */
   RamseteController(double b, double zeta);
 
+  /**
+   * Construct a Ramsete unicycle controller. The default arguments for
+   * b and zeta of 2.0 and 0.7 have been well-tested to produce desireable
+   * results.
+   */
+  RamseteController() : RamseteController(2.0, 0.7) {}
+
   /**
    * Returns true if the pose error is within tolerance of the reference.
    */