Added support for custom port specifications

[Stoo0rmq]

by setting the -p as custom and providing a path to a text file on the -l flag we can read custom lists of ports separated by new lines. This is useful when we are testing against non common http ports or ports that are not in the already existing lists. e.g.

$ echo "127.0.0.1" | ./httprobe -p custom -l ./ports.txt -prefer-https http://127.0.0.1:8443
http://127.0.0.1:8442
http://127.0.0.1

Where ports.txt is a file with different ports , one on every line: 80
81
82
83
8440
8441
8442
8443
8444