Add resquest_phonecall

This Authy::API method is responsible of the following endpoint
/protected/:format/call/:id
Add delete_user

This Authy::API method is responsible of the following endpoint
/protected/:format/users/delete/:id
Update README

Includes the documentation for:

* request phone call
* delete user
Refactor phonecall => phone_call
Update README.md

With travis build status
Update README.md

Add codeclimate badge