Update to 1.6.0
    
    Change build system to CMake. Some tuning to Fedora was required.
    
    Changes:
    - Better TLS connection setup timeout handling, which makes getdns and stubby work better with DoT servers that are slow on initial connection (because they might be under attack).
    
    - Correct handling of UDP Payload size by getdns servers (i.e. listeners)