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