send mail based kue example

make sure started redis-server on localhost:6379

and then
```
cd examples/kuemailer
node index.js
```

open new terminal
```
$ curl -H "Content-Type: application/json" -X POST -d \
    '{
       "type": "postbox",
       "data": {
         "title": "Mangia gli spaghetti con polpette!",
         "to": "mamma.mia@spaghetti.com",
         "template": "newsletter",
         "params": {
            "name": {
              "first": "Mamma",
              "last": "Mia"
            }
         }
       },
       "options" : {
         "attempts": 5,
         "priority": "high"
       }
     }' http://localhost:3000/job

```

PS: mail is not really send, because SMTP config is wrong.