- Added extension priority map. This is an imperfect solution, and is
  not used by default with default configuration (column-based data).

  - We may want to consider a revised columnar format for a future
    version that has a bit more information than is present in the base
    file.

- Adding the sort priority and extension priority helped, but because
  the alphanumeric sort was first in `MIME::Type#priority_compare`, the
  results weren't as good as they should have been. We now sort by the
  sort priority values _first_ and the alphanumeric values _second_.

  - Stored sort priority was not respected because it depends on flags
    not kept in the base file. Added support for a binary file with this
    to ensure it is loaded.