Questionable fix for #17 - deleteByQuery not following API

Questionable fix for the API methods that would require sending a request entity for HTTP methods that technically don't allow request entities.  Fix involves serializing the object that would be passed as the request body, then passing it as the value of the "source" param in the URL query-string.

I personally would prefer for this library to just grit its teeth and send request content where the ES API supports it, btw.

N.B. The only piece of this commit that I've tested against an ES installation is the deleteByQuery method.