new utility object to handle bundle fields

- when using codec config, it can replace string fields that
contain bundle field names without any changes to job configs
- no fussing about with field binder etc or re-binding fields
on every filter
- auto magically caches the last format so that when the format
is fairly consistent, there are no hash look ups on field names
- thread safe (to the extent codec allows - more than enough here)
optionally remove fields w/ bundle filter clear

this is subtlety different than setting them to null
little test for filter test