Addd support for Authy's phone services.

New 3 methods: `verification_start`, `verification_check` and `info`
were added to support authy's phone verification and info services.

Usage:

  authy.phones().verification_start({
      via: "sms",
      country_code: "1",
      phone_number: "111-111-1111"
    }
  );

  authy.phones().verification_check({
      country_code: "1",
      phone_number: "111-111-1111",
      verification_code: "0000"
    }
  );

  authy.phones().info({
      country_code: "1",
      phone_number: "111-111-1111"
    }
  );
Code refactoring, added method to create requests.

A new method `_request` was created to handle GET and POST requests.
This allows us to remove repeated code and improve readability.
Added method for user status end point.

User status returns the status of a user given the id. A new method
`user_status` along with tests were added to support this end point.