[zqxomplg] Assigning numbers to initial letters

Given initial letter frequencies of words (say, from a corpus), assign digits to letters so that the digits are spread out evenly by frequency.  This should be easy (perhaps optimization by simulated annealing.  Need some measure, a norm, of deviation from perfectly evenly distributed).  Standardize this assignment.

Goal is to allow someone to memorize a phrase but type a PIN, making the PINs as uniformly distributed as possible, making it difficult for an attacker to brute force.  The common telephone keypad mapping numbers to letters causes the digits 0 and 1 never to be present in any PINs.