Added Emailrelay package - Version 1.9

As requested by Etienne Champetier champetier.etienne@gmail.com, please see (https://lists.openwrt.org/pipermail/openwrt-devel/2014-July/026632.html)

A previous pull request had been closed since I was on holiday (https://github.com/openwrt/packages/pull/161), I am reopening it with all the changes suggested by KanjiMonster.

From: Federico Di Marco <fededim@gmail.com>

Body of explanation:
A new package has been added in packages feed under net/emailrelay directory, porting a simple SMTP proxy and store-and-forward message transfer agent (MTA) called EmailRelay (please see
http://emailrelay.sourceforge.net/) to OpenWRT.

The patch consists of the following files:

Makefile: standard makefile of OpenWRT packages which downloads from sourceforge the source code and compiles it into a package
files/emailrelay.auth: configuration file for emailrelay
files/emailrelay.init: simple shell script for managing service installation and startup.

Signed-off-by: Federico Di Marco <fededim@gmail.com>