Add --delete-delay DELAY_IN_SECONDS option.

Specifies the number of seconds to wait between deleting
snapshots. Allows ec2-expire-snapshots to run without hitting
the AWS rate limiter.
Undo merged branch changes that did not relate to the branch goal.
trivial re-ordering of options
Add --delete-delay option, thanks to Wayne Robinson (fixes #11 on github) (fixes #12 on github)