Feature/xmltree additions (#20988)

* [change] add/insert/delete family of xmltree expanded with several variations. Added replace methods family

* [change] Lifted child limitations on insert methods (consulted with @araq)

* [tests] add/insert/replace/delete of xmltree XmlNodes tests added

tests/xml/ttree_delete.nim

@@ -0,0 +1,47 @@
+discard """
+  output: '''
+<xml>
+  <head>
+    <div>Some text</div>
+    <div>Some more text </div>
+  </head>
+  <body>
+    <div>Some text in body</div>
+    <div>Some more text in body </div>
+  </body>
+</xml>
+'''
+"""
+
+# Test xmltree add/insert/delete/replace operations
+import xmlparser
+import xmltree
+let initialDocBase = """
+<xml>
+  <head>
+    <div>Some text</div>
+    <div>Some more text </div>
+  </head>
+  <tag>
+    <div>MORE TEXT </div>
+    <div>MORE TEXT Some more text</div>
+  </tag>
+  <tag>
+    <div>MORE TEXT </div>
+    <div>MORE TEXT Some more text</div>
+  </tag>
+  <body>
+    <div>Some text in body</div>
+    <div>Some more text in body </div>
+  </body>
+</xml>
+"""
+var initialDocBaseTree = parseXml(initialDocBase)
+
+proc test_delete() =
+  var testDoc = initialDocBaseTree
+  
+  testDoc.delete(1..2)
+  echo $testDoc
+
+test_delete()