Add the possibility for named parameters in requests

[asciidisco]

I received a mail with a feature request:

I am trying to use your Backbone.rpc to connect my Backbone application to
a JSON-RPC API. (Yes, I am working with a 'rusty old Java developer. 8-) I
notice that when submitting and receiving data, the code uses positional
parameters. Is there a simple way to get it to use named parameters
instead? I have looked over the code and, frankly, some of it is over my
head because I am relatively new to JavaScript and Backbone. After reading
the docs, it wasn't clear to me how or whether this is even possible.

[Pappa]

I've been working through this for a few days too, and it's impossible for me to use Backbone.Rpc without using named parameters. It would definitely be a much needed addition to support the jsonrpc 2.0 spec.

[micrub]

@Pappa Seems like this one were covered by bfd1ef4