Support multiple domains from configuration file

[wyrmiyu]

User should be allowed to define multiple domains in settings.json, where the domain name (current RECORD_NAME) could be a key itself and it's value would be a hash containing USERNAME, PASSWORD, RECORD_ID. Like this:

{
    "recordname1.example.com": {
        "USERNAME": "your_username",
        "PASSWORD": "dns_record_password",
        "RECORD_ID": "dns_record_id"
    },
    "recordname2.example.com": {
        "USERNAME": "your_username",
        "PASSWORD": "dns_record_password",
        "RECORD_ID": "dns_record_id"
    }
}

The script should be updated to loop over all record names in settings.json.