Added initscript and updated the reference config file to include new directives from v0.16 release notes.

I've added a Debian-style initscript to the repository.  It started life as the old, old, old one on the wiki but is now fully Debianized.  It runs rippled as an unprivileged user and group (rippled:rippled).  It specifies the --conf command line switch to the executable so that the installation can be more UNIX-like (config file in /etc/ripple).  It also adds significant functionality (restart, status, ledger status, rippled uptime, server test, and it makes it easier to send arbitrary RPC commands to a running daemon).

I've also added to doc/rippled-example.cfg the directives described in the v0.16 release notes (https://ripple.com/wiki/Latest_rippled_release_notes) which we keep having partners put in their config files anyway.