Some reorganization and the eject method.

The latter tells the library to release the file that was opened. Otherwise,
it never actually closes which can lead to severe problems.
Reorganize the imports and add recorded_at

It would be nice to know when a cassette was recorded. This stores the value
in UTC. When we start accepting the re_record_interval, we can use UTC
timestamps to determine if the cassette is out-of-date regardless of timezone.
Gripe in the comments time
Use the cassette's eject method.

- Reorganize some methods alphabetically.
- Accept the re_record_interval parameter but do nothing with it.