Add HTML Node deep clone implementation

Sources/HTMLNode.m

@@ -668,6 +668,21 @@ NS_INLINE void CheckInvalidCombination(HTMLNode *parent, HTMLNode *node, NSStrin
 
 #endif
 
+#pragma mark - Clone
+
+- (instancetype)cloneNodeDeep:(BOOL)deep
+{
+	HTMLNode *copy = [self copy];
+
+	if (deep) {
+		for (HTMLNode *child in self.childNodes) {
+			[copy appendNode:[child cloneNodeDeep:YES]];
+		}
+	}
+
+	return copy;
+}
+
 #pragma mark - NSCopying
 
 - (id)copyWithZone:(NSZone *)zone

Sources/include/HTMLNode.h

@@ -186,6 +186,14 @@ typedef NS_OPTIONS(unsigned short, HTMLDocumentPosition)
  */
 - (BOOL)isEmpty;
 
+/**
+ Clones this node.
+
+ @param deep If `YES` then also clones child nodes. Otherwise a shallow clone is returned, which behaves the same as `copy`.
+ @return A clone of this node.
+ */
+- (instancetype)cloneNodeDeep:(BOOL)deep;
+
 /**
  Returns the child node at a given index.