option to show all words matching a mask or list of masks

[roycewilliams]

An option could check all words from a given list that match a given list of masks. This helps with analysis of patterns in new founds.

The option could accept either a single mask, or a filename containing masks.

[hops]

A very basic version of this is implemented with commit 654df7d.
We don't support ?h or ?H nor custom mask (yet). Also masks are not really validated as of now. E.g. if you use ?a?a?c it would result in only using ?a?a as filter.
Only one mask (first argument on the command line) is supported. The ability to read multiple masks from a file will be added later.
Example usage:

$ pack2 filtermask ?u?l?l?l?d?d wordlist.txt

As always if no input file is specified it will read from stdin. If no output file (-o, or --output) is specified it writes to stdout.