add skill rust and goal realization/groups

- added a group for skill rust. currently just groups into the different
levels of rust, using the worst rust level found among each unit's
skills
- added a group for goals realized. since it's unknown yet whether or
not unit's can have multiple goals, i've opted to go with a count of
realized goals for now.
- since goal realization is now detected, the goal description has been
updated with 'and that goal was realized' when applicable
- skill rust level can also be checked via scripts. eg d.rust_level() >
0/1/2/3, higher being more rust