Cleanup various things

[xsawyerx]

• Use croak instead of die.
• Explicit minimal import.
• Typo fixes (including two semicolons).
• Correct IO layer to prevent lack of checking.

This is based off master, so if #12 is merged, this should be rebased off that. I would be happy to do that. This can be merged first and then #12 should be rebased. Of course they can both be merged without rebasing but meh.

I leave it as PR in case someone disagrees.