Add getArray method to Dict

This method extend `get`, and will fetch all indirect objects (i.e. `Ref`s) when the result is an `Array`.

src/core/obj.js

@@ -135,6 +135,22 @@ var Dict = (function DictClosure() {
       return Promise.resolve(value);
     },
 
+    // Same as get(), but dereferences all elements if the result is an Array.
+    getArray: function Dict_getArray(key1, key2, key3) {
+      var value = this.get(key1, key2, key3);
+      if (!isArray(value)) {
+        return value;
+      }
+      value = value.slice(); // Ensure that we don't modify the Dict data.
+      for (var i = 0, ii = value.length; i < ii; i++) {
+        if (!isRef(value[i])) {
+          continue;
+        }
+        value[i] = this.xref.fetch(value[i]);
+      }
+      return value;
+    },
+
     // no dereferencing
     getRaw: function Dict_getRaw(key) {
       return this.map[key];