Bronto的php lib和Composer不加载类

I am trying to get the Bronto api PHP lib to work with composers autoload. But no go. What is missing?

Composer.json:

{
    "require": {
        "slim/slim": "2.4.*",
        "bronto/bronto-api-php-client": "dev-master"
    },

    "minimum-stability": "dev"

}

index.php

<?php

require '../vendor/autoload.php';

$app = new \Slim\Slim();

$app->get('/', function () {
    $bronto = new \Bronto_Api();
    $bronto->setToken($token); // Or pass $token to the constructor of Bronto_Api
    $bronto->login(); // Only needs to be called once
});

$app->run();

Slim's framework loads fine. I just keep getting a 'Fatal error: Class 'Bronto_Api' not found in /app/location/'.

Any ideas on what could be going on?

This is 3 years after the original question was asked but I had the same problem trying to add the package to a Laravel project I was working on. I resolved it by adding the following to my composer.json (the one belonging to my project).

"autoload": {
    "psr-0": {
        "Bronto_": "./vendor/bronto/bronto-api-php-client/Symfony/Component/Console/src/"
    }
}

It feels a little dirty but works OK.