Implemented -o,--outfile and cleaned up help text

Outfile functionality allows for specifying a file to directly output the scan
results to. Outfile always outputs verbose. Also, when an outfile is specified,
STDOUT is still output.

Updated helptext with outfile option (-o,--outfile).

Cleaned up helptext so it's more easily maintained.
Implemented --open switch and cleaned up stuff

--open will only check ports that are listed as "open" in the report file being
checked.

Changed parsing methodology in the rescan function so avoid calling pipe, cut,
echo, and bash five times per line

Added documentation for --open to the helptext

Changed output format of scan_all_ports to be only space delimited so it's
easier to parse
Added GPLv3 license

Added header to portscan

Added LICENSE file