The main focus of this commit are changes to fix the handling of html entities. It looks like the conversion from JSON to XML fails to handle characters like " and & properly, so invalid XML is generated. I took the sanitize function from xml2json and reused it for json2xml conversion.

bin/xml2json: adding file from original repo
lib/json2xml: adding latest version and updating with my changes.
lib/xml2json: adding latest version and referencing sanitize from external file.
lib/sanitize.js: moving santize function and characters object to shared file.

- adding sanitize option to toXml output when characters like &, ', " exists.
- fixing issue in santiize function, where it replaces the first instance of the character to replace, to performing a global replace.
- moving sanitize() code to a shared file.