MXS-1220: Add alter maxscale MaxAdmin command

A set of the core MaxScale parameters can now be altered at runtime. This
set consists of the authentication timeouts and the admin interface
authentication. Other parameters either can't be modified due to internal
limitations or aren't sensible to modify at runtime.

Documentation/Reference/MaxAdmin.md

@@ -355,6 +355,8 @@ destroy:
 alter:
     alter server - Alter server parameters
     alter monitor - Alter monitor parameters
+    alter service - Alter service parameters
+    alter maxscale - Alter maxscale parameters
 
 set:
     set server - Set the status of a server
@@ -1583,6 +1585,64 @@ The monitor is stopped and it will be removed on the next restart of MaxScale
 Example: destroy monitor my-monitor
 ```
 
+## Services
+
+### Altering Services
+
+To alter the common service parameters, use the `alter service` command. Module
+specific parameters cannot be altered with this command.
+
+```
+alter service - Alter service parameters
+
+Usage: alter service NAME KEY=VALUE ...
+
+Parameters:
+NAME      Service name
+KEY=VALUE List of `key=value` pairs separated by spaces
+
+All services support the following values for KEY:
+user                          Username used when connecting to servers
+password                      Password used when connecting to servers
+enable_root_user              Allow root user access through this service
+max_retry_interval            Maximum restart retry interval
+max_connections               Maximum connection limit
+connection_timeout            Client idle timeout in seconds
+auth_all_servers              Retrieve authentication data from all servers
+strip_db_esc                  Strip escape characters from database names
+localhost_match_wildcard_host Match wildcard host to 'localhost' address
+version_string                The version string given to client connections
+weightby                      Weighting parameter name
+log_auth_warnings             Log authentication warnings
+retry_on_failure              Retry service start on failure
+
+Example: alter service my-service user=maxuser password=maxpwd
+```
+
+## MaxScale Core
+
+### Altering MaxScale
+
+The core MaxScale parameters that can be modified at runtime can be altered with
+the `alter maxscale` command.
+
+```
+alter maxscale - Alter maxscale parameters
+
+Usage: alter maxscale KEY=VALUE ...
+
+Parameters:
+KEY=VALUE List of `key=value` pairs separated by spaces
+
+The following configuration values can be altered:
+auth_connect_timeout         Connection timeout for permission checks
+auth_read_timeout            Read timeout for permission checks
+auth_write_timeout           Write timeout for permission checks
+admin_auth                   Enable admin interface authentication
+
+Example: alter maxscale auth_connect_timeout=10
+```
+
 ## Other Modules
 
 Modules can implement custom commands called _module commands_. These are