Feature: Scan all possible ports

[tmalaher]

Additionally, for my solution to #11 I expanded the "slow" scan (i.e. fastscan==false) option so it scans all 65536 ports. This does take longer (6.5 minutes in my case) but that is still short enough to be useful. So maybe there are three options instead of two:
fastscan: 72 common ports
mediumscan: 3000+ less common ports
fullcan: all 65536 possible ports