This class implements JSON-RPC 1.1 Procedure Calls according to the 1.1 working
JSON RPC 1.1 requests are never notifications, and accept either hash
references or array references as parameters.
Note that the alternative JSON RPC 1.1 proposition is also be supported:
<http://groups.google.com/group/json-rpc/web/json-rpc-1-1-alt>. kwparams is
accepted as an alias to params, but params will also accept hash
references. However, to simplify things, params and kwparams are mutually
exclusive, since Perl doesnt have strong support for named params.
The alternative spec does not offer notifications (it is a TODO item), so
currently is_notification always returns false.