Fixing text of the Licence.
Tracking object usage.

- Found in github/mime-types at a504206b.
Return an enumerator when no block is given.

- I had apparently missed this lesson of being a good Ruby citizen over
  the last twelve years or so. Regardless, it's a damned fine idea.

- Found in SamSaffron/mime-types at bdc7c442.
Reorganize benchmarking.
Possible change to MIME::Types#type_for