Add support for sparql endpoints

[Panaetius]

It'd be cool if we could point at a sparql endpoint with some query and have the library query the endpoint and deserialize directly.

[suryatejreddy]

Hey, can I work on this issue? I'm currently going through the code and the latest PR #18. Are there any guidelines I need to follow before sending a fix?

[Panaetius]

This issue is not really in a state to be worked on at the moment and needs underlying design work first