List a DKIM and SPF testing tool in the documentation.

Seems like it was removed in nsd4 (since Ubuntu 14.04). It now
silently does nothing.

Fixes #41.

http://pingability.com/zoneinfo.jsp for checking DNS and MX servers.

Added DKIM and SPF testing tool to 'Checking that it worked' section.

move the ssh PasswordAuthentication check to after installing ssh

instead of installing roundcube from Ubuntu (before replacing it), just install the dependencies we need

I had previously awkwardly disabled it because on my VPS the necessary kernel
module wasn't available. I meant to make it an option, but instead I took
out the apt-get install. Now it works for me so I'm putting everything back.

Force the scripts to run in bash

nsd doesn't install without creating the `nsd` user first - merge branch from randallsquared-master, fixes #25

fixes #23

Fix install of php5-cgi, roundcube SQL directory on Ubuntu 14.04

Not sure if I've tested this. Also because of graylisting there's not much of a need
to do sophisticated spam filtering, at least based on the email I get.

DNS test: also check a public nameserver to verify that the registrar (or up-host) configuration is correct too

remove apache before installing nginx --- it's not needed and will start complaining about the port being in use, or it might interfere with nginx

When I re-did this, I left in an old reference to the php-fcgid
script that never made it into the repo. Deleting that and moving
the php-fcgid configuration on top of it.

fixes #9
see 2ebd9706

remove old Amazon EC2-related things since no one should ever deploy a mail server to EC2 (IPs have bad reputation)