better xml building by using xmlbuilder directly

XML (and the freshbooks api), supports child nodes with the same name. XMLBuilder already does a good job building XML request objects, no need to use the limited XMLJS version. I have updated the examples file to show how contacts (and similar objects) should be created (prior to this change, you couldn't add more than one contact). Also updated version to 0.2.0 as changes may not be backwards compatible (depending on how end users implemented this).