Handle hostnames that eTLDService chokes on

Closes #21.

IP Addresses are stored with a reference to a "domain" record with name
"ip_address".

e.g. http://127.0.0.1/...

Other allowed hostnames are stored with a reference to a "domain" record
of "special_hostname".

e.g. http://localhost/...

Other hostnames are considered invalid and ignored.