implementation of DNS relay

functions:

1. forwarding
2. blocking
3. cache

first the program reads a list of cache urls from file url ip-address
when comes a request, it will check whether the requested url is in cache

• if so it will check whether the ip-address is 0.0.0.0
  • if so, the request will be block
  • else return the cached ip-address
• otherwise, it will forward the request to remote server 8.8.8.8 (default)

(optional)
--remoteDNS (ip address of remote DNS)
--dnsListPath (path of cache file format needed (plz see dns-local.txt)