Brand new init methods

Tag class changes:

• New init(_ children: [Tag] = []) init method
• New convenience init(@TagBuilder _ builder: () -> [Tag]) method
• New convenience init(_ contents: String?) method
• New open class func createNode() -> Node function
• New setContents function
• New setAttributes function
• New deleteAttribute function
  New tag base clases:
• EmptyTag
• GroupTag
  New test cases
  Comment tag rendering with spaces