Add option for user to use any file as the word list

[sts10]

I assume this would be good for users who want a passphrase of non-English words.

It is unlikely that the user's list will be uniquely decodable (something I'm a bit of stickler about...), so I'd likely add a check like:

if custom_list.is_some() && separator=="" && !title_case {
   eprintln!("Whether inputted word list is uniquely decodable is unknown. With no separator between words or Title Case, risk of a word overlap too high to proceed.");
}

I think I'd also have Phraze check the inputted list for blank lines and duplicate words.

[sts10]

#14 has finally been merged (for better or worse!).