add a function to filter letters combinations

[amantelli]

as far as i know these would reduce the overall performance for fast hashes dramatically, because the logic of droppping candidates this way is way to slow compared to generating and hashing

on the other hand there is already an optimizer called markov chain for this, which is implemented

thanks for the reply.
Actually I dont see how will be slower overall, considering the number of cominations that would be saved in this way.
I mean, maybe will be slower for <10 char words, but for >10 there is no way this method would slower the normal algo...