Add `Append` method to `HashTable`

sources/Data/Collections/HashTable.uc

@@ -197,6 +197,37 @@ private final function ResizeHashTable(int newSize)
     }
 }
 
+/**
+ *  Appends objects from another `HashTable` to the caller one.
+ *
+ *  @param  other   Array to append objects from. `none` means nothing will be
+ *      added.
+ *  @return Reference to the caller `HashTable` to allow for method chaining.
+ */
+public final function HashTable Append(HashTable other)
+{
+    local AcediaObject      nextKey, nextValue;
+    local HashTableIterator iter;
+
+    if (other == none)          return self;
+    if (other.GetLength() <= 0) return self;
+
+    iter = HashTableIterator(other.Iterate());
+    while (!iter.HasFinished())
+    {
+        nextKey     = iter.GetKey();
+        nextValue   = iter.Get();
+        if (!HasKey(nextKey)) {
+            SetItem(nextKey, nextValue);
+        }
+        _.memory.Free(nextKey);
+        _.memory.Free(nextValue);
+        iter.Next();
+    }
+    _.memory.Free(iter);
+    return self;
+}
+
 /**
  *  Returns minimal capacity of the caller associative array.
  *