Move Implementation-Related details to implementation (api.go) from client.go in client.Receive()

[dattito]

In the Receive() funtion from client.go, a JSON-string is returned. The conversion from a slice to JSON shouldn't be part of the app-layer but part from the implementation-layer.

I would do it myself and then open a pull-request, but then I would have to change something in the json-rpc part of the Receive() function in api.go. And because I am not that in json-rpc, I thought it would be at least good to note it here.

[bbernhard]

Yeah, right, that's definitely something that should be cleaned up at some point. It's actually already on my TODO list, but I haven't found any time yet to fix that.