Make attribute readers private for OSX

There's no reason to have these be public. We aren't using them
anywhere.
Use Tempfile for cached image in OSX test

We don't want to muck with the actual cached image when testing on a
development machine.
Use Tempfile for cached image in CLI test

We don't want to muck with the actual cached image when testing on a
development machine.
Merge pull request #21 from chrishunt/style-me-pretty

Use Tempfile as cached image in tests