Add KeystrokeModifiersAction.

config-serializer/config-items/KeystrokeModifiersAction.ts

@@ -0,0 +1,33 @@
+class KeystrokeModifiersAction extends KeyAction {
+
+    modifierMask: number;
+
+    _fromJsObject(jsObject: any): KeystrokeModifiersAction {
+        this.assertKeyActionType(
+            jsObject, KeyActionType.KeystrokeModifiersAction, 'KeystrokeModifiersAction');
+        this.modifierMask = jsObject.modifierMask;
+        return this;
+    }
+
+    _fromBinary(buffer: UhkBuffer): KeystrokeModifiersAction {
+        this.readAndAssertKeyActionId(buffer, KeyActionId.KeystrokeModifiersAction, 'KeystrokeModifiersAction');
+        this.modifierMask = buffer.readUInt8();
+        return this;
+    }
+
+    _toJsObject(): any {
+        return {
+            keyActionType: KeyActionType.KeystrokeModifiersAction,
+            modifierMask: this.modifierMask
+        };
+    }
+
+    _toBinary(buffer: UhkBuffer) {
+        buffer.writeUInt8(KeyActionId.KeystrokeModifiersAction);
+        buffer.writeUInt8(this.modifierMask);
+    }
+
+    toString(): string {
+        return `<KeystrokeModifiersAction modifierMask="${this.modifierMask}">`;
+    }
+}