Changes to support xml2js

diff --git a/lib/index.js b/lib/index.js
index c05ed36..e4b0e07 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -8,7 +8,37 @@ var auth = require("./auth");
 var util = require("./util");
 var Metadata = require('./metadata');
 var async = require('async');
-var xmlutil = require('xml2json');
+var xml2js = require('xml2js');
+// optional dependency
+try {
+  var xml2json = require('xml2json');
+} catch (er) {
+  xml2json = null;
+}
+
+//utility method to convert to numbers or booleans based on value
+function coerceObject(obj) {
+  if (obj instanceof Object) {
+    for (var property in obj) {
+      if (obj.hasOwnProperty(property)) {
+        obj[property] = coerceObject(obj[property]);
+      }
+    }
+  } else if (typeof(obj) == "string") {
+    var _tmp = Number(obj);
+    if (!isNaN(_tmp)) {
+      return _tmp;
+    }
+    _tmp = obj.toLowerCase();
+    if (_tmp == 'true') {
+      return true;
+    } else if (_tmp == "false") {
+      return false;
+    }
+  }
+  return obj;
+}
+
 
 //public api
 exports.create = exports.load = function(opts, callback) {
@@ -113,10 +143,18 @@ Spreadsheet.prototype.request = function(opts, callback) {
     var result;
 
     try {
-      result = JSON.parse(body);
+      result = JSON.parse(body); // older spreadsheets used a json api
     } catch (e) {
       try {
-        result = JSON.parse(xmlutil.toJson(body));
+        if (xml2json != null) { // xml2json is faster, but requires a native librar
+          result = xml2json.toJson(body, {object: true, sanitize: false, trim: false});
+        } else { // xml2js is all javascript, but is slower and can run out of memory on large sets
+          xml2js.parseString(body, {mergeAttrs: true, charkey: '$t', explicitArray: false}, function(err, res) {
+            if (err) throw err;
+            result = res;
+          });
+          result = coerceObject(result); // xml2js doesn't automatically coerce the datatypes
+        }
       } catch (e) {
         return callback('Bad response format (' + e + ')');
       }
diff --git a/package.json b/package.json
index 3b881cd..2b994b2 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,9 @@
     "request": "~2.21.0",
     "google-oauth-jwt": "0.0.4",
     "async": "~0.2.9",
+    "xml2js": "~0.4.4"
+  },
+  "optionalDependencies": {
     "xml2json": "~0.4.0"
   },
   "repository": "git://github.com/jpillora/node-edit-google-spreadsheet.git"