Update Release Notes and Configuration Guide on MXS_MODULE_PARAM_REGEX

Also added a new Upgrading-To-file with a note on the change.

Documentation/Upgrading/Upgrading-To-MaxScale-2.2.md

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+# Upgrading MariaDB MaxScale from 2.1 to 2.2
+
+This document describes possible issues upgrading MariaDB MaxScale from version
+2.1 to 2.2.
+
+For more information about MariaDB MaxScale 2.2, please refer to the
+[ChangeLog](../Changelog.md).
+
+For a complete list of changes in MaxScale 2.2.0, refer to the
+[MaxScale 2.2.0 Release Notes](../Release-Notes/MaxScale-2.2.0-Release-Notes.md).
+
+Before starting the upgrade, we recommend you back up your current configuration
+file.
+
+### Regular Expression Parameters
+
+Modules may now use a built-in regular expression string parameter type instead
+of a normal string when accepting patterns. The only module using the new regex
+parameter type is currently *QLAFilter*. When inputting pattern, enclose the
+string in slashes, e.g. `match=/^select/` defines the pattern `^select`.