continue implementation; first tests with recursion returned IPs but then added cance...

continue implementation; first tests with recursion returned IPs but then added cancel code

added option to cancel Recursor if timeout is reached
sometimes re-try resolving more quickly instead of calling handle_unavailable
changed saving of ttls: save original value and creation time by adding friend class HostAddress
cache can do the recursive ip retrieval, better place than ResolverBase