Mask attack to recover password

[kimci86]

Work in progress.
Needs more testing and documentation (readme + tutorial update)

This allows to take advantage of knowledge we may have on the password to run faster than bruteforce.
Example for "password123456", if we know the password is 8 lowercase letters followed by 6 digits:

# bruteforce takes several minutes
bkcrack -k 2281be8b 2b08616d d2b8f7a0 --bruteforce ?l?d --length 14

# mask attack takes a second
bkcrack -k 2281be8b 2b08616d d2b8f7a0 -m ?l?l?l?l?l?l?l?l?d?d?d?d?d?d

Closes #55, supersedes #56
Related to #124

You might be interested in trying this @jgrahamc
Binaries can be downloaded from here: https://github.com/kimci86/bkcrack/actions/workflows/ci.yml?query=event%3Apull_request+branch%3Amask

[jgrahamc]

Thanks. I will try this. Although I think I'm starting to hit the limits of what's possible with the hardware I have. I've so far run to completion:

?p up to 14 characters
?u?d up to 15 characters
?u up to 17 characters

It's slow going!