Plan:
  - Deleting
  - Tied interface
  - Special handling for duplicate keys (error, share, overwrite, separate)
  - add a callback for elements lost in max_count overflow
  - _make should probably also do the followup call. the current way is too
    error prone
  - The "self-absorb" test may in fact give false positives on systems where
    addresses can be so big they don't fit in an NV with full resolution.