Redis has a lot of commands, users can use those commands to access
redis data.People get to know the commands by reading redis document
(https://redis.io/commands) .

Redis module is a wonderful feature which make it possible for user
to create custom commands.But when a module is loaded in redis, we
don't know what commands in the module, unless we have read the
module's source code or the module released with document.

A brief description about the module and the commands in the module
is needed.So the new module subcommand 'module desc' is very useful.
The module and its commands' brief description will be shown to
users by run 'module desc name'.

In order to make the module subcommand work properly, module developers
should provide the module description when call RedisModule_Init and
function description when call  RedisModule_CreateCommand.

A new desc parameter added to RedisModule_Init,so the function changed
to:
    int RedisModule_Init(RedisModuleCtx *ctx, const char *modulename,
		         const char *moduledesc,int module_version,
		         int api_version);

A new desc parameter added to RedisModule_CreateCommand, so the function
changed to:
    int RedisModule_CreateCommand(RedisModuleCtx *ctx, const char *cmdname,
		          const char *cmddesc,RedisModuleCmdFunc cmdfunc);