minimal UDP DNS proxy completed
TCP upstream support
reuse upstream connections
better DNSClient repr
rename
allow multiple filters
split DNSClient into UDPDNSClient and TCPDNSClient
filter bad IPs
reorder
renamed again...
TODO bogus_nxdomain auto detecting
check all primary_clients for bogus nxdomain
use upstreams instead of clients to avoid confusion
minor update
fallover to secondary when poisoned
minor update
match DNS id
handle timeout
minor fix
handle exception correctly