json2xml: Fix/update to match earlier changes in xml2json.
You can now do round trips xml -> json -> xml and end up
with the same xml as you started. (In some cases white space
will differ.)

xml2json: add quotes around the keys in the output json.
This is especially important when there is an @ or # character
in the key.
Fix toXml() optional arguments to a method that also works in node.