Added json-rpc support

Added JsonRpcMethod and RpcParam annotations.
Provided annotations handling

Usage:

``` java
public interface JsonRpcApi {
  @JsonRpcMethod("get_user_info")
  void bootstrapAsync(@RpcParam("user") String user, Callback<ResponseData> data);
}
```

``` java
RestAdapter restAdapter =
     new RestAdapter.Builder().setConverter(new JsonRpcConverter(this.gson))
           .setExecutors(httpExecutor, resultExecutor)
           .setEndpoint(String.format("http://%s:%d/api/", Const.SERVER, Const.PORT)).build();
JsonRpcApi api = restAdapter.create(JsonRpcApi.class);
```