cdata deserialization test and implementation

Hey, 

Great repo, was a joy to use for coding on a wordpress xml-rpc interface emulator project :)
I noticed CDATA was not being deserialized, but instead resulted in empty fields;
So i wrote a test and implemented the very small fix necessary to implement it.

I guess this could be of use to other people as well, so here's a pull-request ...

best,
simon