/**
* Parses xml to json using node-expat.
* @param {String|Buffer} xml The xml to be parsed to json.
* @param {Object} _options An object with options provided by the user.
* The available options are:
* - object: If true, the parser returns a Javascript object instead of
* a JSON string.
* - reversible: If true, the parser generates a reversible JSON, mainly
* characterized by the presence of the property $t.
* - sanitize_values: If true, the parser escapes any element value in the xml
* that has any of the following characters: <, >, (, ), #, #, &, ", '.