Added class DOM\Exception - DOM module exception class
Added class DOM\Source\Pointer\XPath - Represents data for DOMXPath object
Added class DOM\Source\XPath - Getting data from DOM objects by XPath
Added class DOM\Iterator\Node - Recursive DOMNode iterator for iteration over DOM objects
Added class DOM\ToArray - For extracting DOM objects to array
Added class DOM\ToDOMNodeList - For extracting DOM objects to DOMNodeList

Added tests: DOM_Source_XPathTest, DOM_ToArrayTest, DOM_ToDOMNodeList