Rename love.audio.setMixMode to setMixWithSystem. Fix some copyright notice typos.

--HG--
branch : minor

src/modules/audio/Audio.h

@@ -9,7 +9,7 @@
  * including commercial applications, and to alter it and redistribute it
  * freely, subject to the following restrictions:
  *
- * 1. The origin of this software must not be misrepresented = 0; you must not
+ * 1. The origin of this software must not be misrepresented; you must not
  *    claim that you wrote the original software. If you use this software
  *    in a product, an acknowledgment in the product documentation would be
  *    appreciated but is not required.
@@ -256,6 +256,12 @@ public:
 	 */
 	virtual bool isEFXsupported() const = 0;
 
+	/**
+	 * Sets whether audio from other apps mixes with love.audio or is muted,
+	 * on supported platforms.
+	 **/
+	bool setMixWithSystem(bool mix);
+
 private:
 
 	static StringMap<DistanceModel, DISTANCE_MAX_ENUM>::Entry distanceModelEntries[];