Use Guzzle instead of Buzz

This PR is related to https://github.com/sensiolabs/connect/pull/48. I've not tested anything (no tests are currently provided) but it should work ;)

 - [ ] Remove dependency on my custom repo and update once the other PR has been merged
 - [ ] Update README, bump version
 - [ ] Use array of option on API constructor instead of guzzle object
 - [ ] Add a "replay with curl" command, see 

```html
               <th>Replay with Curl</th>
               <td>
                   <pre><code>curl "{{ call.request.url }}" -X {{ call.request.method}} {% for header in call.request.headers %}-H "{{ header }}" {% endfor %}{% if call.request.content %}--data "{{ call.request.content }}"{% endif %} </code></pre>
               </td>
```
We should better inject option than guzzle http client here