Support for new end points.

This pull request contains 3 "big" changes:
1. Added support for new end points.
2. Code refactoring.
3. Tests format change. 


Please find below more details.
1. Authy has exposed the new API end points:

  - Start phone verification (POST /protected/json/phones/verification/start)
  - Check phone verification (GET /protected/json/phones/verification/check)
  - Phone information (GET /protected/json/phones/info)
  - User status (GET /protected/json/users/:user_id/status)

  The phone related methods were encapsulated in the Authy.phone() method. For instance, to call the Start Phone Verification method you need to do:

  ```javascript
  authy.phone().verification_start({
    via: "sms",
    country_code: "1",
    phone_number: "111-111-1111"
  }, function(err, res) {
    // Stuff
  } );
  ```


2. A new method (authy._request) was added to handle all the requests (POST and GET) and we use it instead of calling the request object.


3. In the other hand, the format for the tests added was modified for readability.
Instead of hiding this function with an _ I'd rather it just be named and not attached to the prototype since its just for internal use. 

Use .bind to maintain the `this` state or properly call it with the fully built options.