TODO

* multi-threading - use pthread.h?
* can't handle wildcarded domains that return more than one IP address on
  non-existing subdomains
      test domain: proboards.com
* allow using a customized list of DNS server to share network load
* allow using DNS server supplied on the command line
* for openDNS users: document how to permanently change DNS server
  settings so they are not overwritten by DHCP settings
* convert hostent structs to addrinfo ?
* replace inet_ntoa(*((struct in_addr *)host->h_addr_list[j])) with ipstr
* obtain aliases for each domain (CNAME records)?
* clever numerical domain bruteforce for clusters. i.e.: www2, www3
* pickup new subdomains via reverse lookups (PTR records)
* better input validation
      improve function that validates target domain