Revise domain creation to allow select arguments
Revise domain creation to allow select arguments

Previously, passing `$spamAction` only worked if an SMTP password (`$smtpPass`) was provided. This revision de-couples those two arguments.

In addition, it adds support for the `$wildcard` arguments (which appeared to not be used before).

Finally, this revision adds SMTP password validation (the same used in the `credentials` method).

mailgun/mailgun-php,michabbb-backup/mailgun-php