Fix up some dumb mistakes in S3Provider

Was performing :with_prefix, :delete, etc. directly against the
S3Bucket instance, instead of its ObjectCollection.  Which of course
won't actually work.

Fixed up.
Fix mistake in Kernel.spawn call

Was calling spawn with a list of args, instead of splatting that
list as spawn would prefer.  Fixed.
Fix calls to Kernel#system

Revised system calls to splat the lists of args instead of just
passing the arg list along.
S3 keys should not begin with a slash

The S3 keys get awkward in context if they start with a leading slash,
like they do when they come straight from the URI path.

Strip off the leading slash, and now they're nice and happy.
auto-consul executable and README

Now a fun time can be head with the auto-consul executable,
and the README.md gives some examples of how stuff works.