Move combine effect constants to class enum, not global scope

effect_combine.h

-/* Audio Library for Teensy 3.X
- * Copyright (c) 2014, Paul Stoffregen, paul@pjrc.com
+/* Copyright (c) 2018 John-Michael Reed
+ * bleeplabs.com
  *
  * Development of this audio library was funded by PJRC.COM, LLC by sales of
  * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
- 
-   Combine analog signals with bitwise expressions like OXR. Combining two simple oscillators results in interesting new waveforms, 
-   Combining white noise or dynamic incoming audio results in aggressive digital distortion.
- 
+ *
+ * Combine analog signals with bitwise expressions like XOR.
+ * Combining two simple oscillators results in interesting new waveforms,
+ * Combining white noise or dynamic incoming audio results in aggressive digital distortion.
  */
 
 #ifndef effect_digital_combine_h_
 #include <Arduino.h>
 #include "AudioStream.h"
 
-#define OR      0
-#define XOR  1
-#define AND    2
-#define MODULO  3
-
 class AudioEffectDigitalCombine : public AudioStream
 {
 public:
+	enum combineMode {
+		OR    = 0,
+		XOR   = 1,
+		AND   = 2,
+		MODULO = 3,
+	};
 	AudioEffectDigitalCombine() : AudioStream(2, inputQueueArray), mode_sel(OR) { }
-	void mode(short mode_in) {
+	void setCombineMode(int mode_in) {
 		if (mode_in > 3) {
 	  		mode_in = 3;
 	  	}