Calling a method to add a nested element returns the parent element, and not the newly nested element.  This makes it impossible to reference the newly created element and makes all of the helper functions (like AddDial) useless because you have to new up a Dial element to have access to it anyway.

Fix is to return the nested element instead of 'this'.
Merge pull request #3 from mikdav/PlivoXmlFixes

Fixing an issue when adding nested elements