ability to mute a sequence

fixes #823

Tone/event/Sequence.test.ts

@@ -299,6 +299,17 @@ describe("Sequence", () => {
 			});
 		});
 
+		it("can mute the callback", () => {
+			return Offline(({ transport }) => {
+				const seq = new Sequence(() => {
+					throw new Error("shouldn't call this callback");
+				}, [0, 0.1, 0.2, 0.3]).start();
+				seq.mute = true;
+				expect(seq.mute).to.be.true;
+				transport.start();
+			}, 0.5);
+		});
+
 	});
 
 	context("Looping", () => {

Tone/event/Sequence.ts

@@ -102,7 +102,7 @@ export class Sequence<ValueType = any> extends ToneEvent<ValueType> {
 	 * The internal callback for when an event is invoked
 	 */
 	private _seqCallback(time: Seconds, value: any): void {
-		if (value !== null) {
+		if (value !== null && !this.mute) {
 			this.callback(time, value);
 		}
 	}