add new option: --format-flag=+xxxx,+yyyy,-zzzz

This will allow john to 'adjust' the format. So a 'generic' format may handle uc/lc, handle lengths up to 125 byte password. BUT a pen tester may have inside knowledge that a set of hashes are NOT generic. Say for instance that it is known that the input is lc utf8 compliant data, truncated to 8 bytes. The generic format can be used, but we can tweak it's flags, so that it works better.

So in this case, we may do things like: --max-length=8 (not sure about this, due to utf8), --format-flag=+trunc,-case,+utf8

Then if things like rules would be used (for this format), specifying --rules-stack=:l would force password to lc