Some optimizations: Calculate values in setup instead of in innner loop

[htgoebel]

• Zero-base columns internally, which avoids some calculations for every line.
• Pre-calculate prefixes, which avoids calculating them for each IP address.
• Format log messages only when actually output

[htgoebel]

@open-dynaMIX I updated the code to use dicts. Read to merge IMHO.

[open-dynaMIX]

Great, thanks a lot @htgoebel!