Adding the date in the Response object

It would help to go further with extensions if the date was available in a convenient format in the Response object.

``` coffeescript
bot.on 'user:join', (r) ->
  if r.time.hour is > 11
    r.reply "You are late #{r.nick} !"
```

Check the Cinch API for an example, every Message instance (which is similar to our Response object) include a Time (ruby) object.
