Add dragonbones api about armatureKey, which is regard as 'dragonbone…

…sName' (#4100)

* Add dragonbones  api about armatureKey, which is regard as dragonbonesName.

* Add dragonbones  api about armatureKey, which is regard as dragonbonesName.

extensions/dragonbones/ArmatureDisplay.js

@@ -451,6 +451,21 @@ let ArmatureDisplay = cc.Class({
         this._updateDebugDraw();
     },
 
+    /**
+     * !#en
+     * The key of dragonbones cache data, which is regard as 'dragonbonesName', when you want to change dragonbones cloth.
+     * !#zh 
+     * 缓存龙骨数据的key值，换装的时会使用到该值，作为dragonbonesName使用
+     * @method getArmatureKey
+     * @example
+     * let factory = dragonBones.CCFactory.getInstance();
+     * let needChangeSlot = needChangeArmature.armature().getSlot("changeSlotName");
+     * factory.replaceSlotDisplay(toChangeArmature.getArmatureKey(), "armatureName", "slotName", "displayName", needChangeSlot);
+     */
+    getArmatureKey () {
+        return this._armatureKey;
+    },
+
     onRestore () {
         // Destroyed and restored in Editor
         if (!this._material) {
@@ -469,7 +484,7 @@ let ArmatureDisplay = cc.Class({
      * 
      * @method setAnimationCacheMode
      * @param {AnimationCacheMode} cacheMode
-     * * @example
+     * @example
      * armatureDisplay.setAnimationCacheMode(dragonBones.ArmatureDisplay.AnimationCacheMode.SHARED_CACHE);
      */
     setAnimationCacheMode (cacheMode) {