XmlOutputFormat does not escape all required symbols in case of attribte/text

[snuyanzin]

Currently it escapes only " and < while & also must be escaped in case of attribute/text based on [1].
At the same time both " and ' are not required to be encoded for case of element text while for xml attribute one of them should be depending on attribute quote type.
Also > must be escaped if there is a sequence ]]> inside text or attribute value which is not a part of CDATA

[1] https://www.w3.org/TR/2008/REC-xml-20081126/#syntax

[julianhyde]

Fixed in 2cee6c7, PR #110. Thanks @snuyanzin!