Updated CMake files -- added libunbound linker flag

CMake config file written, but was unable to test/get it working
properly because of a bug in CMake with functions related to
find_package.  Simple "-lunbound" flag used in its stead for now.  May
not build on non-Linux systems, not sure yet.
ipv4 and ipv6 resolution working

IPv4 and IPv6 name resolution working.
Unit tests written (and passing).
net_node.{h,inl} code modified to use DNS seeds.