Added 1.3 to 1.4 upgrade guide

The guide explains the changes in encryption and SSL.

Documentation/Upgrading/Upgrading-To-MaxScale-1.4.md

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+# Upgrading MaxScale from 1.3 to 1.4
+
+This document describes upgrading MaxScale from version 1.3 to 1.4.
+
+For more detailed information, please refer to the [release notes](../Release-Notes/MaxScale-1.4.0-Release-Notes.md).
+
+## Installation
+
+Before starting the upgrade, we **strongly** recommend you back up your current
+configuration file.
+
+## Password encryption
+
+MaxScale 1.4.0 upgrades the used password encryption algorithms to more secure ones.
+This requires that the password files are recreated with the `maxkeys` tool.
+For more information about how to do this, please read the installation guide:
+[MariaDB MaxScale Installation Guide](../Documentation/Getting-Started/MariaDB-MaxScale-Installation-Guide.md)
+
+## SSL
+
+The SSL configuration parameters are now a part of the listeners. If a service
+used the old style SSL configuration parameters, the values should be moved to
+the listener which is associated with that service.
+
+Here is an example of an old style configuration.
+
+```
+[RW Split Router]
+type=service
+router=readwritesplit
+servers=server1,server2,server3,server4
+user=jdoe
+passwd=BD26E4139A15280CA882264AA1551C70
+ssl=required
+ssl_cert=/home/user/certs/server-cert.pem
+ssl_key=/home/user/certs/server-key.pem
+ssl_ca_cert=/home/user/certs/ca.pem
+ssl_version=TLSv12
+
+[RW Split Listener]
+type=listener
+service=RW Split Router
+protocol=MySQLClient
+port=3306
+```
+
+And here is the new, 1.4.0 compatible configuration style.
+
+```
+[RW Split Router]
+type=service
+router=readwritesplit
+servers=server1,server2,server3,server4
+user=jdoe
+passwd=BD26E4139A15280CA882264AA1551C70
+
+[RW Split Listener]
+type=listener
+service=RW Split Router
+protocol=MySQLClient
+port=3306
+ssl=required
+ssl_cert=/home/user/certs/server-cert.pem
+ssl_key=/home/user/certs/server-key.pem
+ssl_ca_cert=/home/user/certs/ca.pem
+ssl_version=TLSv12
+```
+
+Please also note that the `enabled` SSL mode is no longer supported due to
+the inherent security issues with allowing SSL and non-SSL connections on
+the same port. In addition to this, SSLv3 is no longer supported due to
+vulnerabilities found in it.