New port: security/py-xkcdpass

A flexible and scriptable password generator which generates
strong diceword-style passphrases, inspired by XKCD 936.

$ xkcdpass
> correct horse battery staple

Usable as standalone script or a module within a larger
Python project.

WWW: https://github.com/jwfh/xkcdpass

Submitted by: jacob_jwfh.ca
Differential Revision: https://reviews.freebsd.org/D21234