Algorithm improvements

1. Compute score of each numeric and alphanumeric word in text (possibly all non-words -- this will be harder)
2. Adjust scores for each plausible code in a given message based on proximity of the keywords. 
3. Adjust score based on length (for example, it's unlikely that the code is < 3 chars and > 6-8 chars.)

Choose highest score out of plausible codes.