Adds full registration support

* Method Snapchat::register now takes the user's email, password and
birth date.
* New method Snapchat::getCaptcha that gets captcha ID and files.
* New method Snapchat::solveCaptcha that sends a solution to a captcha.
* New method Snapchat::registerUsername that associates an username with
the account.
* ZIP decompression no longer leaks temporary files.