Agent runners use optional :advertise IP.

For https://github.com/ethanrowe/auto-consul/issues/5

The AutoConsul::Runner module ::agent_runner and ::server_runner
singleton methods both allow for an option hash at the end, within
which one may provide an :advertise IP addr to use with the
consul `-advertise` option.

This allows us to advertise a different IP than that to which
we're bound.
Entry point script options for bind/advertise

bin/auto-consul options:
* "-a" now sets both the bind and advertise IPs.
* "-b"/"--bind" sets just the bind address (0.0.0.0 by default)
* "--advertise" sets just the advertise address (no default specified)

Both the runner and the heartbeat function make use of this.
Merge remote-tracking branch 'origin/advertise-support'
Bump gem version to 0.0.3

To reflect changes in runner and entry point opts in support of
https://github.com/ethanrowe/auto-consul/issues/5