[NEW] Enable error logging

`index.php` file

```php
<?php

require '../vendor/autoload.php';

use \Norm\Norm;
use \Bono\App;
use \Flynsarmy\SlimMonolog\Log\MonologWriter;
use \Monolog\Handler\StreamHandler;

$app = new App(array(
    'autorun' => false,
    'mode'    => 'development',
    'log.enabled' => true,
    'log.writer'  => new MonologWriter(array(
        'handlers' => array(
            new StreamHandler('../logs/'.date('d-M-Y').'.log')
        ),
    )),
));

$app->get('/', function () use ($app) {
    // Will throw error
    $app->urlFor('xxx');
    $app->view->render('hello');
});

$app->run();
```

I want to log the error to somewhere, but the `zeuxisoo/slim-whoops` package cannot log the error, I must write the log first before exception being handled by `$app->config('whoops')->handleException($exception);`. By this patch, we can log error message to the log by Monolog. The SlimFramework hook before app and before controller only get the request log, not the error.

```php
$app->error(function ($exception) use ($app) {
    // Log error if it's enabled
    if ($app->config('log.enabled')) {
        $app->log->error((string) $exception);
    }
    // Throw whoops exception
    $app->config('whoops')->handleException($exception);
});
```

Log:
```
[2014-04-21 11:58:40] SlimMonoLogger.ERROR: exception 'RuntimeException' with message 'Named route not found for name: xxx' in /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Router.php:187 Stack trace: #0 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Slim.php(1069): Slim\Router->urlFor('xxx', Array) #1 /home/alfa/workspaces/internal/development/www/index.php(23): Slim\Slim->urlFor('xxx') #2 [internal function]: {closure}() #3 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Route.php(436): call_user_func_array(Object(Closure), Array) #4 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Slim.php(1307): Slim\Route->dispatch() #5 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Middleware/Flash.php(85): Slim\Slim->call() #6 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Middleware/MethodOverride.php(92): Slim\Middleware\Flash->call() #7 /home/alfa/workspaces/internal/bono/src/Bono/Middleware/ControllerMiddleware.php(94): Slim\Middleware\MethodOverride->call() #8 /home/alfa/workspaces/internal/bono/src/Bono/Middleware/ContentNegotiatorMiddleware.php(75): Bono\Middleware\ControllerMiddleware->call() #9 /home/alfa/workspaces/internal/bono/src/Bono/Middleware/WhoopsMiddleware.php(87): Bono\Middleware\ContentNegotiatorMiddleware->call() #10 /home/alfa/workspaces/internal/bono/src/Bono/Middleware/CommonHandlerMiddleware.php(65): Bono\Middleware\WhoopsMiddleware->call() #11 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Middleware/PrettyExceptions.php(67): Bono\Middleware\CommonHandlerMiddleware->call() #12 /home/alfa/workspaces/internal/development/vendor/slim/slim/Slim/Slim.php(1254): Slim\Middleware\PrettyExceptions->call() #13 /home/alfa/workspaces/internal/bono/src/Bono/App.php(269): Slim\Slim->run() #14 /home/alfa/workspaces/internal/development/www/index.php(27): Bono\App->run() #15 {main} [] []
```

![bonologger](https://cloud.githubusercontent.com/assets/3734729/2752556/93c542a8-c912-11e3-8d66-5895aa64a32c.png)

The Whoops Pretty page still working:

![whoopserror](https://cloud.githubusercontent.com/assets/3734729/2752576/4d26981e-c913-11e3-800f-501a6e8ed0eb.png)

Also I don't know, but composer cannot find `"filp/whoops": "1"`, so I change the version to the latest one.