Request cancelation

Use WaspRequest as return type and take the advantage of features such as cancel.

    @GET("/repos/{user}/{repo}")
    WaspRequest getRepo(
           @Path("user") String user,
           @Path("repo") String repo,
           Callback<Repo> callback
    );


    WaspRequest request = service.getRepo();
    request.cancel();

for multiple requests, use the request manager to cancel all request at once

private final RequestManager requestManager = new SimpleRequestManager();

public void onRefreshData(){
   WaspRequest request = service.getData();
   requestManager.addRequest(request);
}

public void onAnotherNetworkCall() {
   WaspRequest request = service.getFoo();
   requestManager.addRequest(request);
}

public void onDestroy(){
   requestManager.cancelAll();
}